Add .NET 6 target (#2677)

Build/build.ps1

@@ -32,7 +32,8 @@
   $nunitConsolePath = "$buildDir\Temp\NUnit.ConsoleRunner.$nunitConsoleVersion"
 
   $builds = @(
-    @{Framework = "netstandard2.0"; TestsFunction = "NetCliTests"; TestFramework = "net6.0"; Enabled=$true},
+    @{Framework = "net6.0"; TestsFunction = "NetCliTests"; TestFramework = "net6.0"; Enabled=$true},
+    @{Framework = "netstandard2.0"; TestsFunction = "NetCliTests"; TestFramework = "net5.0"; Enabled=$true},
     @{Framework = "netstandard1.3"; TestsFunction = "NetCliTests"; TestFramework = "netcoreapp3.1"; Enabled=$true},
     @{Framework = "netstandard1.0"; TestsFunction = "NetCliTests"; TestFramework = "netcoreapp2.1"; Enabled=$true},
     @{Framework = "net45"; TestsFunction = "NUnitTests"; TestFramework = "net46"; NUnitFramework="net-4.0"; Enabled=$true},

Src/Newtonsoft.Json.Tests/Linq/JObjectTests.cs

@@ -1439,7 +1439,7 @@ Parameter name: arrayIndex",
             ITypedList l = new JObject(p1, p2);
 
             PropertyDescriptorCollection propertyDescriptors = l.GetItemProperties(null);
-            Assert.IsNull(propertyDescriptors);
+            Assert.AreEqual(0, propertyDescriptors.Count);
         }
 
         [Test]

Src/Newtonsoft.Json.Tests/Newtonsoft.Json.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks Condition="'$(TestFrameworks)'==''">net46;net40;net35;net20;net6.0;netcoreapp3.1;netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks Condition="'$(TestFrameworks)'==''">net46;net40;net35;net20;net5.0;net6.0;netcoreapp3.1;netcoreapp2.1</TargetFrameworks>
     <TargetFrameworks Condition="'$(TestFrameworks)'!=''">$(TestFrameworks)</TargetFrameworks>
     <LangVersion>9.0</LangVersion>
     <VersionPrefix>1.0</VersionPrefix>
@@ -13,7 +13,7 @@
     <RootNamespace>Newtonsoft.Json.Tests</RootNamespace>
     <IsPackable>false</IsPackable>
     <!-- Workaround for https://github.com/nunit/nunit3-vs-adapter/issues/296 -->
-    <DebugType Condition="'$(TargetFramework)' != '' AND '$(TargetFramework)' != 'netcoreapp2.1' AND '$(TargetFramework)' != 'netcoreapp3.1' AND '$(TargetFramework)' != 'net6.0'">Full</DebugType>    
+    <DebugType Condition="'$(TargetFramework)' != '' AND '$(TargetFramework)' != 'netcoreapp2.1' AND '$(TargetFramework)' != 'netcoreapp3.1' AND '$(TargetFramework)' != 'net5.0' AND '$(TargetFramework)' != 'net6.0'">Full</DebugType>    
     <!-- Disabled because SourceLink isn't referenced to calculate paths -->
     <DeterministicSourcePaths>false</DeterministicSourcePaths>
     <!-- It's ok if a test target has exited support. Disable NETSSDK1138 warning -->
@@ -109,6 +109,27 @@
     <DefineConstants>NET20;$(AdditionalConstants)</DefineConstants>
   </PropertyGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)'=='net5.0'">
+    <PackageReference Include="BenchmarkDotNet" Version="$(BenchmarkDotNetPackageVersion)" />
+    <PackageReference Include="FSharp.Core" Version="$(FSharpCorePackageVersion)" />
+    <PackageReference Include="System.ObjectModel" Version="$(SystemObjectModelPackageVersion)" />
+    <PackageReference Include="System.Runtime.Serialization.Primitives" Version="$(SystemRuntimeSerializationPrimitivesPackageVersion)" />
+    <PackageReference Include="System.Runtime.Serialization.Xml" Version="$(SystemRuntimeSerializationXmlPackageVersion)" />
+    <PackageReference Include="System.Runtime.Serialization.Formatters" Version="$(SystemRuntimeSerializationFormattersPackageVersion)" />
+    <PackageReference Include="System.Xml.XmlSerializer" Version="$(SystemXmlXmlDocumentPackageVersion)" />
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTuplePackageVersion)" />
+    <PackageReference Include="Autofac" Version="$(AutofacPackageVersion)" />
+    <PackageReference Include="Moq" Version="$(MoqPackageVersion)" />
+    <PackageReference Include="xunit" Version="$(XunitPackageVersion)" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="$(XunitRunnerVisualStudioPackageVersion)" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(MicrosoftNETTestSdkPackageVersion)" />
+  </ItemGroup>
+  <PropertyGroup Condition="'$(TargetFramework)'=='net5.0'">
+    <AssemblyTitle>Json.NET Tests .NET Standard 2.0</AssemblyTitle>
+    <ReferringTargetFrameworkForProjectReferences>.NETStandard,Version=v2.0</ReferringTargetFrameworkForProjectReferences>
+    <DefineConstants>NETSTANDARD2_0;DNXCORE50;PORTABLE;HAVE_BENCHMARKS;HAVE_REGEX_TIMEOUTS;$(AdditionalConstants)</DefineConstants>
+  </PropertyGroup>
+
   <ItemGroup Condition="'$(TargetFramework)'=='net6.0'">
     <PackageReference Include="BenchmarkDotNet" Version="$(BenchmarkDotNetPackageVersion)" />
     <PackageReference Include="FSharp.Core" Version="$(FSharpCorePackageVersion)" />
@@ -125,8 +146,8 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(MicrosoftNETTestSdkPackageVersion)" />
   </ItemGroup>
   <PropertyGroup Condition="'$(TargetFramework)'=='net6.0'">
-    <AssemblyTitle>Json.NET Tests .NET Standard 2.0</AssemblyTitle>
-    <ReferringTargetFrameworkForProjectReferences>.NETStandard,Version=v2.0</ReferringTargetFrameworkForProjectReferences>
+    <AssemblyTitle>Json.NET Tests .NET 6.0</AssemblyTitle>
+    <ReferringTargetFrameworkForProjectReferences>net6.0</ReferringTargetFrameworkForProjectReferences>
     <DefineConstants>NETSTANDARD2_0;DNXCORE50;PORTABLE;HAVE_BENCHMARKS;HAVE_REGEX_TIMEOUTS;$(AdditionalConstants)</DefineConstants>
   </PropertyGroup>
 

Src/Newtonsoft.Json/Converters/BinaryConverter.cs

@@ -126,7 +126,7 @@ namespace Newtonsoft.Json.Converters
             {
                 // current token is already at base64 string
                 // unable to call ReadAsBytes so do it the old fashion way
-                string encodedData = reader.Value!.ToString();
+                string encodedData = reader.Value!.ToString()!;
                 data = Convert.FromBase64String(encodedData);
             }
             else
@@ -135,7 +135,7 @@ namespace Newtonsoft.Json.Converters
             }
 
             Type t = (ReflectionUtils.IsNullableType(objectType))
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
 
 #if HAVE_LINQ

Src/Newtonsoft.Json/Converters/DataSetConverter.cs

@@ -84,7 +84,7 @@ namespace Newtonsoft.Json.Converters
             // handle typed datasets
             DataSet ds = (objectType == typeof(DataSet))
                 ? new DataSet()
-                : (DataSet)Activator.CreateInstance(objectType);
+                : (DataSet)Activator.CreateInstance(objectType)!;
 
             DataTableConverter converter = new DataTableConverter();
 
@@ -92,7 +92,7 @@ namespace Newtonsoft.Json.Converters
 
             while (reader.TokenType == JsonToken.PropertyName)
             {
-                DataTable dt = ds.Tables[(string)reader.Value!];
+                DataTable? dt = ds.Tables[(string)reader.Value!];
                 bool exists = (dt != null);
 
                 dt = (DataTable)converter.ReadJson(reader, typeof(DataTable), dt, serializer)!;

Src/Newtonsoft.Json/Converters/DataTableConverter.cs

@@ -99,7 +99,7 @@ namespace Newtonsoft.Json.Converters
                 // handle typed datasets
                 dt = (objectType == typeof(DataTable))
                     ? new DataTable()
-                    : (DataTable)Activator.CreateInstance(objectType);
+                    : (DataTable)Activator.CreateInstance(objectType)!;
             }
 
             // DataTable is inside a DataSet
@@ -144,7 +144,7 @@ namespace Newtonsoft.Json.Converters
 
                 reader.ReadAndAssert();
 
-                DataColumn column = dt.Columns[columnName];
+                DataColumn? column = dt.Columns[columnName];
                 if (column == null)
                 {
                     Type columnType = GetColumnDataType(reader);
@@ -185,7 +185,7 @@ namespace Newtonsoft.Json.Converters
                         reader.ReadAndAssert();
                     }
 
-                    Array destinationArray = Array.CreateInstance(column.DataType.GetElementType(), o.Count);
+                    Array destinationArray = Array.CreateInstance(column.DataType.GetElementType()!, o.Count);
                     ((IList)o).CopyTo(destinationArray, 0);
 
                     dr[columnName] = destinationArray;

Src/Newtonsoft.Json/Converters/DiscriminatedUnionConverter.cs

@@ -182,7 +182,7 @@ namespace Newtonsoft.Json.Converters
 
             while (reader.TokenType == JsonToken.PropertyName)
             {
-                string propertyName = reader.Value!.ToString();
+                string propertyName = reader.Value!.ToString()!;
                 if (string.Equals(propertyName, CasePropertyName, StringComparison.OrdinalIgnoreCase))
                 {
                     reader.ReadAndAssert();

Src/Newtonsoft.Json/Converters/EntityKeyMemberConverter.cs

@@ -129,7 +129,7 @@ namespace Newtonsoft.Json.Converters
             reader.ReadAndAssert();
             string? type = reader.Value?.ToString();
 
-            Type t = Type.GetType(type);
+            Type t = Type.GetType(type!)!;
 
             ReadAndAssertProperty(reader, ValuePropertyName);
             reader.ReadAndAssert();

Src/Newtonsoft.Json/Converters/ExpandoObjectConverter.cs

@@ -119,7 +119,7 @@ namespace Newtonsoft.Json.Converters
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string propertyName = reader.Value!.ToString();
+                        string propertyName = reader.Value!.ToString()!;
 
                         if (!reader.Read())
                         {

Src/Newtonsoft.Json/Converters/IsoDateTimeConverter.cs

@@ -133,7 +133,7 @@ namespace Newtonsoft.Json.Converters
 
 #if HAVE_DATE_TIME_OFFSET
             Type t = (nullable)
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
 #endif
 
@@ -167,6 +167,8 @@ namespace Newtonsoft.Json.Converters
                 return null;
             }
 
+            MiscellaneousUtils.Assert(dateText != null);
+
 #if HAVE_DATE_TIME_OFFSET
             if (t == typeof(DateTimeOffset))
             {

Src/Newtonsoft.Json/Converters/JavaScriptDateTimeConverter.cs

@@ -98,7 +98,7 @@ namespace Newtonsoft.Json.Converters
 
 #if HAVE_DATE_TIME_OFFSET
             Type t = (ReflectionUtils.IsNullableType(objectType))
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
             if (t == typeof(DateTimeOffset))
             {

Src/Newtonsoft.Json/Converters/KeyValuePairConverter.cs

@@ -102,7 +102,7 @@ namespace Newtonsoft.Json.Converters
             reader.ReadAndAssert();
 
             Type t = ReflectionUtils.IsNullableType(objectType)
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
 
             ReflectionObject reflectionObject = ReflectionObjectPerType.Get(t);
@@ -111,7 +111,7 @@ namespace Newtonsoft.Json.Converters
 
             while (reader.TokenType == JsonToken.PropertyName)
             {
-                string propertyName = reader.Value!.ToString();
+                string propertyName = reader.Value!.ToString()!;
                 if (string.Equals(propertyName, KeyName, StringComparison.OrdinalIgnoreCase))
                 {
                     reader.ReadForTypeAndAssert(keyContract, false);
@@ -145,7 +145,7 @@ namespace Newtonsoft.Json.Converters
         public override bool CanConvert(Type objectType)
         {
             Type t = (ReflectionUtils.IsNullableType(objectType))
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
 
             if (t.IsValueType() && t.IsGenericType())

Src/Newtonsoft.Json/Converters/RegexConverter.cs

@@ -179,7 +179,7 @@ namespace Newtonsoft.Json.Converters
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string propertyName = reader.Value!.ToString();
+                        string propertyName = reader.Value!.ToString()!;
 
                         if (!reader.Read())
                         {

Src/Newtonsoft.Json/Converters/StringEnumConverter.cs

@@ -222,7 +222,7 @@ namespace Newtonsoft.Json.Converters
             }
 
             bool isNullable = ReflectionUtils.IsNullableType(objectType);
-            Type t = isNullable ? Nullable.GetUnderlyingType(objectType) : objectType;
+            Type t = isNullable ? Nullable.GetUnderlyingType(objectType)! : objectType;
 
             try
             {
@@ -267,7 +267,7 @@ namespace Newtonsoft.Json.Converters
         public override bool CanConvert(Type objectType)
         {
             Type t = (ReflectionUtils.IsNullableType(objectType))
-                ? Nullable.GetUnderlyingType(objectType)
+                ? Nullable.GetUnderlyingType(objectType)!
                 : objectType;
 
             return t.IsEnum();

Src/Newtonsoft.Json/Converters/UnixDateTimeConverter.cs

@@ -144,7 +144,7 @@ namespace Newtonsoft.Json.Converters
                 DateTime d = UnixEpoch.AddSeconds(seconds);
 
 #if HAVE_DATE_TIME_OFFSET
-                Type t = (nullable)
+                Type? t = (nullable)
                     ? Nullable.GetUnderlyingType(objectType)
                     : objectType;
                 if (t == typeof(DateTimeOffset))

Src/Newtonsoft.Json/Converters/XmlNodeConverter.cs

@@ -79,19 +79,19 @@ namespace Newtonsoft.Json.Converters
             return new XmlNodeWrapper(_document.CreateSignificantWhitespace(text));
         }
 
-        public IXmlNode CreateXmlDeclaration(string? version, string? encoding, string? standalone)
+        public IXmlNode CreateXmlDeclaration(string version, string? encoding, string? standalone)
         {
             return new XmlDeclarationWrapper(_document.CreateXmlDeclaration(version, encoding, standalone));
         }
 
 #if HAVE_XML_DOCUMENT_TYPE
-        public IXmlNode CreateXmlDocumentType(string? name, string? publicId, string? systemId, string? internalSubset)
+        public IXmlNode CreateXmlDocumentType(string name, string? publicId, string? systemId, string? internalSubset)
         {
             return new XmlDocumentTypeWrapper(_document.CreateDocumentType(name, publicId, systemId, null));
         }
 #endif
 
-        public IXmlNode CreateProcessingInstruction(string target, string? data)
+        public IXmlNode CreateProcessingInstruction(string target, string data)
         {
             return new XmlNodeWrapper(_document.CreateProcessingInstruction(target, data));
         }
@@ -114,7 +114,7 @@ namespace Newtonsoft.Json.Converters
             return attribute;
         }
 
-        public IXmlNode CreateAttribute(string qualifiedName, string namespaceUri, string? value)
+        public IXmlNode CreateAttribute(string qualifiedName, string? namespaceUri, string? value)
         {
             XmlNodeWrapper attribute = new XmlNodeWrapper(_document.CreateAttribute(qualifiedName, namespaceUri));
             attribute.Value = value;
@@ -153,7 +153,7 @@ namespace Newtonsoft.Json.Converters
             _element.SetAttributeNode((XmlAttribute)xmlAttributeWrapper.WrappedNode!);
         }
 
-        public string GetPrefixOfNamespace(string namespaceUri)
+        public string? GetPrefixOfNamespace(string namespaceUri)
         {
             return _element.GetPrefixOfNamespace(namespaceUri);
         }
@@ -171,15 +171,15 @@ namespace Newtonsoft.Json.Converters
             _declaration = declaration;
         }
 
-        public string Version => _declaration.Version;
+        public string? Version => _declaration.Version;
 
-        public string Encoding
+        public string? Encoding
         {
             get => _declaration.Encoding;
             set => _declaration.Encoding = value;
         }
 
-        public string Standalone
+        public string? Standalone
         {
             get => _declaration.Standalone;
             set => _declaration.Standalone = value;
@@ -199,11 +199,11 @@ namespace Newtonsoft.Json.Converters
 
         public string Name => _documentType.Name;
 
-        public string System => _documentType.SystemId;
+        public string? System => _documentType.SystemId;
 
-        public string Public => _documentType.PublicId;
+        public string? Public => _documentType.PublicId;
 
-        public string InternalSubset => _documentType.InternalSubset;
+        public string? InternalSubset => _documentType.InternalSubset;
 
         public override string? LocalName => "DOCTYPE";
     }
@@ -285,7 +285,7 @@ namespace Newtonsoft.Json.Converters
                     }
                     else
                     {
-                        _attributes = new List<IXmlNode>(_node.Attributes.Count);
+                        _attributes = new List<IXmlNode>(_node.Attributes!.Count);
                         foreach (XmlAttribute attribute in _node.Attributes)
                         {
                             _attributes.Add(WrapNode(attribute));
@@ -314,7 +314,7 @@ namespace Newtonsoft.Json.Converters
         {
             get
             {
-                XmlNode node = _node is XmlAttribute attribute ? attribute.OwnerElement : _node.ParentNode;
+                XmlNode? node = _node is XmlAttribute attribute ? attribute.OwnerElement : _node.ParentNode;
 
                 if (node == null)
                 {
@@ -354,38 +354,38 @@ namespace Newtonsoft.Json.Converters
         IXmlNode CreateCDataSection(string? data);
         IXmlNode CreateWhitespace(string? text);
         IXmlNode CreateSignificantWhitespace(string? text);
-        IXmlNode CreateXmlDeclaration(string? version, string? encoding, string? standalone);
+        IXmlNode CreateXmlDeclaration(string version, string? encoding, string? standalone);
 #if HAVE_XML_DOCUMENT_TYPE
-        IXmlNode CreateXmlDocumentType(string? name, string? publicId, string? systemId, string? internalSubset);
+        IXmlNode CreateXmlDocumentType(string name, string? publicId, string? systemId, string? internalSubset);
 #endif
-        IXmlNode CreateProcessingInstruction(string target, string? data);
+        IXmlNode CreateProcessingInstruction(string target, string data);
         IXmlElement CreateElement(string elementName);
         IXmlElement CreateElement(string qualifiedName, string namespaceUri);
-        IXmlNode CreateAttribute(string name, string? value);
-        IXmlNode CreateAttribute(string qualifiedName, string namespaceUri, string? value);
+        IXmlNode CreateAttribute(string name, string value);
+        IXmlNode CreateAttribute(string qualifiedName, string namespaceUri, string value);
 
         IXmlElement? DocumentElement { get; }
     }
 
     internal interface IXmlDeclaration : IXmlNode
     {
-        string Version { get; }
-        string Encoding { get; set; }
-        string Standalone { get; set; }
+        string? Version { get; }
+        string? Encoding { get; set; }
+        string? Standalone { get; set; }
     }
 
     internal interface IXmlDocumentType : IXmlNode
     {
         string Name { get; }
-        string System { get; }
-        string Public { get; }
-        string InternalSubset { get; }
+        string? System { get; }
+        string? Public { get; }
+        string? InternalSubset { get; }
     }
 
     internal interface IXmlElement : IXmlNode
     {
         void SetAttributeNode(IXmlNode attribute);
-        string GetPrefixOfNamespace(string namespaceUri);
+        string? GetPrefixOfNamespace(string namespaceUri);
         bool IsEmpty { get; }
     }
 
@@ -417,15 +417,15 @@ namespace Newtonsoft.Json.Converters
 
         public override XmlNodeType NodeType => XmlNodeType.XmlDeclaration;
 
-        public string Version => Declaration.Version;
+        public string? Version => Declaration.Version;
 
-        public string Encoding
+        public string? Encoding
         {
             get => Declaration.Encoding;
             set => Declaration.Encoding = value;
         }
 
-        public string Standalone
+        public string? Standalone
         {
             get => Declaration.Standalone;
             set => Declaration.Standalone = value;
@@ -444,11 +444,11 @@ namespace Newtonsoft.Json.Converters
 
         public string Name => _documentType.Name;
 
-        public string System => _documentType.SystemId;
+        public string? System => _documentType.SystemId;
 
-        public string Public => _documentType.PublicId;
+        public string? Public => _documentType.PublicId;
 
-        public string InternalSubset => _documentType.InternalSubset;
+        public string? InternalSubset => _documentType.InternalSubset;
 
         public override string? LocalName => "DOCTYPE";
     }
@@ -491,40 +491,40 @@ namespace Newtonsoft.Json.Converters
 
         public IXmlNode CreateComment(string? text)
         {
-            return new XObjectWrapper(new XComment(text));
+            return new XObjectWrapper(new XComment(text!));
         }
 
         public IXmlNode CreateTextNode(string? text)
         {
-            return new XObjectWrapper(new XText(text));
+            return new XObjectWrapper(new XText(text!));
         }
 
         public IXmlNode CreateCDataSection(string? data)
         {
-            return new XObjectWrapper(new XCData(data));
+            return new XObjectWrapper(new XCData(data!));
         }
 
         public IXmlNode CreateWhitespace(string? text)
         {
-            return new XObjectWrapper(new XText(text));
+            return new XObjectWrapper(new XText(text!));
         }
 
         public IXmlNode CreateSignificantWhitespace(string? text)
         {
-            return new XObjectWrapper(new XText(text));
+            return new XObjectWrapper(new XText(text!));
         }
 
-        public IXmlNode CreateXmlDeclaration(string? version, string? encoding, string? standalone)
+        public IXmlNode CreateXmlDeclaration(string version, string? encoding, string? standalone)
         {
             return new XDeclarationWrapper(new XDeclaration(version, encoding, standalone));
         }
 
-        public IXmlNode CreateXmlDocumentType(string? name, string? publicId, string? systemId, string? internalSubset)
+        public IXmlNode CreateXmlDocumentType(string name, string? publicId, string? systemId, string? internalSubset)
         {
             return new XDocumentTypeWrapper(new XDocumentType(name, publicId, systemId, internalSubset));
         }
 
-        public IXmlNode CreateProcessingInstruction(string target, string? data)
+        public IXmlNode CreateProcessingInstruction(string target, string data)
         {
             return new XProcessingInstructionWrapper(new XProcessingInstruction(target, data));
         }
@@ -540,12 +540,12 @@ namespace Newtonsoft.Json.Converters
             return new XElementWrapper(new XElement(XName.Get(localName, namespaceUri)));
         }
 
-        public IXmlNode CreateAttribute(string name, string? value)
+        public IXmlNode CreateAttribute(string name, string value)
         {
             return new XAttributeWrapper(new XAttribute(name, value));
         }
 
-        public IXmlNode CreateAttribute(string qualifiedName, string namespaceUri, string? value)
+        public IXmlNode CreateAttribute(string qualifiedName, string namespaceUri, string value)
         {
             string localName = MiscellaneousUtils.GetLocalName(qualifiedName);
             return new XAttributeWrapper(new XAttribute(XName.Get(localName, namespaceUri), value));
@@ -590,7 +590,7 @@ namespace Newtonsoft.Json.Converters
         public override string? Value
         {
             get => Text.Value;
-            set => Text.Value = value;
+            set => Text.Value = value ?? string.Empty;
         }
 
         public override IXmlNode? ParentNode
@@ -619,7 +619,7 @@ namespace Newtonsoft.Json.Converters
         public override string? Value
         {
             get => Text.Value;
-            set => Text.Value = value;
+            set => Text.Value = value ?? string.Empty;
         }
 
         public override IXmlNode? ParentNode
@@ -650,7 +650,7 @@ namespace Newtonsoft.Json.Converters
         public override string? Value
         {
             get => ProcessingInstruction.Data;
-            set => ProcessingInstruction.Data = value;
+            set => ProcessingInstruction.Data = value ?? string.Empty;
         }
     }
 
@@ -807,7 +807,7 @@ namespace Newtonsoft.Json.Converters
         public override string? Value
         {
             get => Attribute.Value;
-            set => Attribute.Value = value;
+            set => Attribute.Value = value ?? string.Empty;
         }
 
         public override string? LocalName => Attribute.Name.LocalName;
@@ -919,14 +919,14 @@ namespace Newtonsoft.Json.Converters
         public override string? Value
         {
             get => Element.Value;
-            set => Element.Value = value;
+            set => Element.Value = value ?? string.Empty;
         }
 
         public override string? LocalName => Element.Name.LocalName;
 
         public override string? NamespaceUri => Element.Name.NamespaceName;
 
-        public string GetPrefixOfNamespace(string namespaceUri)
+        public string? GetPrefixOfNamespace(string namespaceUri)
         {
             return Element.GetPrefixOfNamespace(namespaceUri);
         }
@@ -1059,7 +1059,7 @@ namespace Newtonsoft.Json.Converters
                     {
                         if (attribute.NamespaceUri == "http://www.w3.org/2000/xmlns/" && attribute.LocalName != "xmlns")
                         {
-                            manager.AddNamespace(attribute.LocalName, attribute.Value);
+                            manager.AddNamespace(attribute.LocalName!, attribute.Value!);
                         }
                     }
                 }
@@ -1078,7 +1078,7 @@ namespace Newtonsoft.Json.Converters
             }
             else
             {
-                return XmlConvert.DecodeName(node.LocalName);
+                return XmlConvert.DecodeName(node.LocalName)!;
             }
         }
 
@@ -1131,7 +1131,7 @@ namespace Newtonsoft.Json.Converters
             {
                 if (attribute.LocalName == "Array" && attribute.NamespaceUri == JsonNamespaceUri)
                 {
-                    return XmlConvert.ToBoolean(attribute.Value);
+                    return XmlConvert.ToBoolean(attribute.Value!);
                 }
             }
 
@@ -1201,7 +1201,7 @@ namespace Newtonsoft.Json.Converters
                         }
                         else
                         {
-                            if (!nodesGroupedByName.TryGetValue(currentNodeName, out object value))
+                            if (!nodesGroupedByName.TryGetValue(currentNodeName, out object? value))
                             {
                                 nodesGroupedByName.Add(currentNodeName, childNode);
                             }
@@ -1314,7 +1314,7 @@ namespace Newtonsoft.Json.Converters
                             if (attribute.NamespaceUri == "http://www.w3.org/2000/xmlns/")
                             {
                                 string namespacePrefix = (attribute.LocalName != "xmlns")
-                                    ? XmlConvert.DecodeName(attribute.LocalName)
+                                    ? XmlConvert.DecodeName(attribute.LocalName)!
                                     : string.Empty;
                                 string? namespaceUri = attribute.Value;
                                 if (namespaceUri == null)
@@ -1654,7 +1654,7 @@ namespace Newtonsoft.Json.Converters
                         case JsonTypeReflector.TypePropertyName:
                         case JsonTypeReflector.ValuePropertyName:
                             string attributeName = propertyName.Substring(1);
-                            string attributePrefix = manager.LookupPrefix(JsonNamespaceUri);
+                            string? attributePrefix = manager.LookupPrefix(JsonNamespaceUri);
                             AddAttribute(reader, document, currentNode, propertyName, attributeName, manager, attributePrefix);
                             return;
                     }
@@ -1685,7 +1685,9 @@ namespace Newtonsoft.Json.Converters
                     string encodedName = XmlConvert.EncodeName(nameValue.Key);
                     string? attributePrefix = MiscellaneousUtils.GetPrefix(nameValue.Key);
 
-                    IXmlNode attribute = (!StringUtils.IsNullOrEmpty(attributePrefix)) ? document.CreateAttribute(encodedName, manager.LookupNamespace(attributePrefix) ?? string.Empty, nameValue.Value) : document.CreateAttribute(encodedName, nameValue.Value);
+                    IXmlNode attribute = (!StringUtils.IsNullOrEmpty(attributePrefix))
+                        ? document.CreateAttribute(encodedName, manager.LookupNamespace(attributePrefix) ?? string.Empty, nameValue.Value!)
+                        : document.CreateAttribute(encodedName, nameValue.Value!);
 
                     element.SetAttributeNode(attribute);
                 }
@@ -1731,10 +1733,10 @@ namespace Newtonsoft.Json.Converters
             }
 
             string encodedName = XmlConvert.EncodeName(attributeName);
-            string? attributeValue = ConvertTokenToXmlValue(reader);
+            string attributeValue = ConvertTokenToXmlValue(reader)!;
 
             IXmlNode attribute = (!StringUtils.IsNullOrEmpty(attributePrefix))
-                ? document.CreateAttribute(encodedName, manager.LookupNamespace(attributePrefix), attributeValue)
+                ? document.CreateAttribute(encodedName, manager.LookupNamespace(attributePrefix)!, attributeValue)
                 : document.CreateAttribute(encodedName, attributeValue);
 
             ((IXmlElement)currentNode).SetAttributeNode(attribute);
@@ -1874,7 +1876,7 @@ namespace Newtonsoft.Json.Converters
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string attributeName = reader.Value!.ToString();
+                        string attributeName = reader.Value!.ToString()!;
 
                         if (!StringUtils.IsNullOrEmpty(attributeName))
                         {
@@ -1896,7 +1898,7 @@ namespace Newtonsoft.Json.Converters
 
                                     if (IsNamespaceAttribute(attributeName, out string? namespacePrefix))
                                     {
-                                        manager.AddNamespace(namespacePrefix, attributeValue);
+                                        manager.AddNamespace(namespacePrefix, attributeValue!);
                                     }
                                     break;
                                 case '$':
@@ -1909,7 +1911,7 @@ namespace Newtonsoft.Json.Converters
                                         case JsonTypeReflector.ValuePropertyName:
                                             // check that JsonNamespaceUri is in scope
                                             // if it isn't then add it to document and namespace manager
-                                            string jsonPrefix = manager.LookupPrefix(JsonNamespaceUri);
+                                            string? jsonPrefix = manager.LookupPrefix(JsonNamespaceUri);
                                             if (jsonPrefix == null)
                                             {
                                                 if (attributeNameValues == null)
@@ -2008,12 +2010,17 @@ namespace Newtonsoft.Json.Converters
                     }
                 }
 
+                if (version == null)
+                {
+                    throw JsonSerializationException.Create(reader, "Version not specified for XML declaration.");
+                }
+
                 IXmlNode declaration = document.CreateXmlDeclaration(version, encoding, standalone);
                 currentNode.AppendChild(declaration);
             }
             else
             {
-                IXmlNode instruction = document.CreateProcessingInstruction(propertyName.Substring(1), ConvertTokenToXmlValue(reader));
+                IXmlNode instruction = document.CreateProcessingInstruction(propertyName.Substring(1), ConvertTokenToXmlValue(reader)!);
                 currentNode.AppendChild(instruction);
             }
         }
@@ -2050,6 +2057,11 @@ namespace Newtonsoft.Json.Converters
                 }
             }
 
+            if (name == null)
+            {
+                throw JsonSerializationException.Create(reader, "Name not specified for XML document type.");
+            }
+
             IXmlNode documentType = document.CreateXmlDocumentType(name, publicId, systemId, internalSubset);
             currentNode.AppendChild(documentType);
         }
@@ -2058,7 +2070,7 @@ namespace Newtonsoft.Json.Converters
         private IXmlElement CreateElement(string elementName, IXmlDocument document, string? elementPrefix, XmlNamespaceManager manager)
         {
             string encodeName = EncodeSpecialCharacters ? XmlConvert.EncodeLocalName(elementName) : XmlConvert.EncodeName(elementName);
-            string ns = StringUtils.IsNullOrEmpty(elementPrefix) ? manager.DefaultNamespace : manager.LookupNamespace(elementPrefix);
+            string? ns = StringUtils.IsNullOrEmpty(elementPrefix) ? manager.DefaultNamespace : manager.LookupNamespace(elementPrefix);
 
             IXmlElement element = (!StringUtils.IsNullOrEmpty(ns)) ? document.CreateElement(encodeName, ns) : document.CreateElement(encodeName);
 
@@ -2077,7 +2089,7 @@ namespace Newtonsoft.Json.Converters
                             throw JsonSerializationException.Create(reader, "JSON root object has multiple properties. The root object must have a single property in order to create a valid XML document. Consider specifying a DeserializeRootElementName.");
                         }
 
-                        string propertyName = reader.Value!.ToString();
+                        string propertyName = reader.Value!.ToString()!;
                         reader.ReadAndAssert();
 
                         if (reader.TokenType == JsonToken.StartArray)
@@ -2092,7 +2104,7 @@ namespace Newtonsoft.Json.Converters
                             if (count == 1 && WriteArrayAttribute)
                             {
                                 MiscellaneousUtils.GetQualifiedNameParts(propertyName, out string? elementPrefix, out string localName);
-                                string ns = StringUtils.IsNullOrEmpty(elementPrefix) ? manager.DefaultNamespace : manager.LookupNamespace(elementPrefix);
+                                string? ns = StringUtils.IsNullOrEmpty(elementPrefix) ? manager.DefaultNamespace : manager.LookupNamespace(elementPrefix);
 
                                 foreach (IXmlNode childNode in currentNode.ChildNodes)
                                 {
@@ -2110,7 +2122,7 @@ namespace Newtonsoft.Json.Converters
                         }
                         continue;
                     case JsonToken.StartConstructor:
-                        string constructorName = reader.Value!.ToString();
+                        string constructorName = reader.Value!.ToString()!;
 
                         while (reader.Read() && reader.TokenType != JsonToken.EndConstructor)
                         {

Src/Newtonsoft.Json/JsonConvert.cs

@@ -302,7 +302,7 @@ namespace Newtonsoft.Json
 
         private static string EnsureDecimalPlace(double value, string text)
         {
-            if (double.IsNaN(value) || double.IsInfinity(value) || text.IndexOf('.') != -1 || text.IndexOf('E') != -1 || text.IndexOf('e') != -1)
+            if (double.IsNaN(value) || double.IsInfinity(value) || StringUtils.IndexOf(text, '.') != -1 || StringUtils.IndexOf(text, 'E') != -1 || StringUtils.IndexOf(text, 'e') != -1)
             {
                 return text;
             }
@@ -312,7 +312,7 @@ namespace Newtonsoft.Json
 
         private static string EnsureDecimalPlace(string text)
         {
-            if (text.IndexOf('.') != -1)
+            if (StringUtils.IndexOf(text, '.') != -1)
             {
                 return text;
             }

Src/Newtonsoft.Json/JsonReader.cs

@@ -496,7 +496,7 @@ namespace Newtonsoft.Json
                     }
                     else
                     {
-                        s = v is Uri uri ? uri.OriginalString : v.ToString();
+                        s = v is Uri uri ? uri.OriginalString : v.ToString()!;
                     }
 
                     SetToken(JsonToken.String, s, false);
@@ -940,7 +940,7 @@ namespace Newtonsoft.Json
             if (Value != null && Value.ToString() == JsonTypeReflector.TypePropertyName)
             {
                 ReaderReadAndAssert();
-                if (Value != null && Value.ToString().StartsWith("System.Byte[]", StringComparison.Ordinal))
+                if (Value != null && Value.ToString()!.StartsWith("System.Byte[]", StringComparison.Ordinal))
                 {
                     ReaderReadAndAssert();
                     if (Value.ToString() == JsonTypeReflector.ValuePropertyName)

Src/Newtonsoft.Json/JsonTextReader.Async.cs

@@ -79,7 +79,7 @@ namespace Newtonsoft.Json
                         return ParseObjectAsync(cancellationToken);
                     case State.PostValue:
                         Task<bool> task = ParsePostValueAsync(false, cancellationToken);
-                        if (task.IsCompletedSucessfully())
+                        if (task.IsCompletedSuccessfully())
                         {
                             if (task.Result)
                             {
@@ -542,7 +542,7 @@ namespace Newtonsoft.Json
             _charPos++;
 
             Task<bool> task = EnsureCharsAsync(1, append, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 SetNewLine(task.Result);
                 return AsyncUtils.CompletedTask;
@@ -1680,7 +1680,7 @@ namespace Newtonsoft.Json
             if (Value != null && Value.ToString() == JsonTypeReflector.TypePropertyName)
             {
                 await ReaderReadAndAssertAsync(cancellationToken).ConfigureAwait(false);
-                if (Value != null && Value.ToString().StartsWith("System.Byte[]", StringComparison.Ordinal))
+                if (Value != null && Value.ToString()!.StartsWith("System.Byte[]", StringComparison.Ordinal))
                 {
                     await ReaderReadAndAssertAsync(cancellationToken).ConfigureAwait(false);
                     if (Value.ToString() == JsonTypeReflector.ValuePropertyName)

Src/Newtonsoft.Json/JsonTextReader.cs

@@ -2353,6 +2353,7 @@ namespace Newtonsoft.Json
         {
             if (setToken)
             {
+                MiscellaneousUtils.Assert(_chars != null);
                 SetToken(JsonToken.Comment, new string(_chars, initialPosition, endPosition - initialPosition));
             }
         }

Src/Newtonsoft.Json/JsonTextWriter.Async.cs

@@ -190,7 +190,7 @@ namespace Newtonsoft.Json
         private Task WriteValueInternalAsync(JsonToken token, string value, CancellationToken cancellationToken)
         {
             Task task = InternalWriteValueAsync(token, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return _writer.WriteAsync(value, cancellationToken);
             }
@@ -270,7 +270,7 @@ namespace Newtonsoft.Json
         private Task WriteIntegerValueAsync(ulong uvalue, bool negative, CancellationToken cancellationToken)
         {
             Task task = InternalWriteValueAsync(JsonToken.Integer, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return WriteDigitsAsync(uvalue, negative, cancellationToken);
             }
@@ -321,13 +321,13 @@ namespace Newtonsoft.Json
         internal Task DoWritePropertyNameAsync(string name, CancellationToken cancellationToken)
         {
             Task task = InternalWritePropertyNameAsync(name, cancellationToken);
-            if (!task.IsCompletedSucessfully())
+            if (!task.IsCompletedSuccessfully())
             {
                 return DoWritePropertyNameAsync(task, name, cancellationToken);
             }
 
             task = WriteEscapedStringAsync(name, _quoteName, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return _writer.WriteAsync(':', cancellationToken);
             }
@@ -399,7 +399,7 @@ namespace Newtonsoft.Json
         internal Task DoWriteStartArrayAsync(CancellationToken cancellationToken)
         {
             Task task = InternalWriteStartAsync(JsonToken.StartArray, JsonContainerType.Array, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return _writer.WriteAsync('[', cancellationToken);
             }
@@ -429,7 +429,7 @@ namespace Newtonsoft.Json
         internal Task DoWriteStartObjectAsync(CancellationToken cancellationToken)
         {
             Task task = InternalWriteStartAsync(JsonToken.StartObject, JsonContainerType.Object, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return _writer.WriteAsync('{', cancellationToken);
             }
@@ -481,7 +481,7 @@ namespace Newtonsoft.Json
         internal Task DoWriteUndefinedAsync(CancellationToken cancellationToken)
         {
             Task task = InternalWriteValueAsync(JsonToken.Undefined, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return _writer.WriteAsync(JsonConvert.Undefined, cancellationToken);
             }
@@ -1058,7 +1058,7 @@ namespace Newtonsoft.Json
         internal Task DoWriteValueAsync(string? value, CancellationToken cancellationToken)
         {
             Task task = InternalWriteValueAsync(JsonToken.String, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return value == null ? _writer.WriteAsync(JsonConvert.Null, cancellationToken) : WriteEscapedStringAsync(value, true, cancellationToken);
             }
@@ -1193,7 +1193,7 @@ namespace Newtonsoft.Json
         internal Task WriteValueNotNullAsync(Uri value, CancellationToken cancellationToken)
         {
             Task task = InternalWriteValueAsync(JsonToken.String, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return WriteEscapedStringAsync(value.OriginalString, true, cancellationToken);
             }
@@ -1314,7 +1314,7 @@ namespace Newtonsoft.Json
         {
             UpdateScopeWithFinishedValue();
             Task task = AutoCompleteAsync(JsonToken.Undefined, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return WriteRawAsync(json, cancellationToken);
             }

Src/Newtonsoft.Json/JsonTextWriter.cs

@@ -325,6 +325,7 @@ namespace Newtonsoft.Json
 
             int newLineLen = SetIndentChars();
 
+            MiscellaneousUtils.Assert(_indentChars != null);
             _writer.Write(_indentChars, 0, newLineLen + Math.Min(currentIndentCount, IndentCharBufferSize));
 
             while ((currentIndentCount -= IndentCharBufferSize) > 0)
@@ -637,6 +638,7 @@ namespace Newtonsoft.Json
             {
                 int length = WriteValueToBuffer(value);
 
+                MiscellaneousUtils.Assert(_writeBuffer != null);
                 _writer.Write(_writeBuffer, 0, length);
             }
             else
@@ -692,6 +694,7 @@ namespace Newtonsoft.Json
             {
                 int length = WriteValueToBuffer(value);
 
+                MiscellaneousUtils.Assert(_writeBuffer != null);
                 _writer.Write(_writeBuffer, 0, length);
             }
             else
@@ -829,6 +832,8 @@ namespace Newtonsoft.Json
             else
             {
                 int length = WriteNumberToBuffer(value, negative);
+
+                MiscellaneousUtils.Assert(_writeBuffer != null);
                 _writer.Write(_writeBuffer, 0, length);
             }
         }
@@ -887,6 +892,8 @@ namespace Newtonsoft.Json
             else
             {
                 int length = WriteNumberToBuffer(value, negative);
+
+                MiscellaneousUtils.Assert(_writeBuffer != null);
                 _writer.Write(_writeBuffer, 0, length);
             }
         }

Src/Newtonsoft.Json/JsonWriter.Async.cs

@@ -291,7 +291,7 @@ namespace Newtonsoft.Json
                 if (_currentState == State.Property)
                 {
                     t = WriteNullAsync(cancellationToken);
-                    if (!t.IsCompletedSucessfully())
+                    if (!t.IsCompletedSuccessfully())
                     {
                         return AwaitProperty(t, levelsToComplete, token, cancellationToken);
                     }
@@ -302,7 +302,7 @@ namespace Newtonsoft.Json
                     if (_currentState != State.ObjectStart && _currentState != State.ArrayStart)
                     {
                         t = WriteIndentAsync(cancellationToken);
-                        if (!t.IsCompletedSucessfully())
+                        if (!t.IsCompletedSuccessfully())
                         {
                             return AwaitIndent(t, levelsToComplete, token, cancellationToken);
                         }
@@ -310,7 +310,7 @@ namespace Newtonsoft.Json
                 }
 
                 t = WriteEndAsync(token, cancellationToken);
-                if (!t.IsCompletedSucessfully())
+                if (!t.IsCompletedSuccessfully())
                 {
                     return AwaitEnd(t, levelsToComplete, cancellationToken);
                 }
@@ -691,10 +691,10 @@ namespace Newtonsoft.Json
                     return WriteStartArrayAsync(cancellationToken);
                 case JsonToken.StartConstructor:
                     ValidationUtils.ArgumentNotNull(value, nameof(value));
-                    return WriteStartConstructorAsync(value.ToString(), cancellationToken);
+                    return WriteStartConstructorAsync(value.ToString()!, cancellationToken);
                 case JsonToken.PropertyName:
                     ValidationUtils.ArgumentNotNull(value, nameof(value));
-                    return WritePropertyNameAsync(value.ToString(), cancellationToken);
+                    return WritePropertyNameAsync(value.ToString()!, cancellationToken);
                 case JsonToken.Comment:
                     return WriteCommentAsync(value?.ToString(), cancellationToken);
                 case JsonToken.Integer:

Src/Newtonsoft.Json/JsonWriter.cs

@@ -537,11 +537,11 @@ namespace Newtonsoft.Json
                     break;
                 case JsonToken.StartConstructor:
                     ValidationUtils.ArgumentNotNull(value, nameof(value));
-                    WriteStartConstructor(value.ToString());
+                    WriteStartConstructor(value.ToString()!);
                     break;
                 case JsonToken.PropertyName:
                     ValidationUtils.ArgumentNotNull(value, nameof(value));
-                    WritePropertyName(value.ToString());
+                    WritePropertyName(value.ToString()!);
                     break;
                 case JsonToken.Comment:
                     WriteComment(value?.ToString());

Src/Newtonsoft.Json/Linq/Extensions.cs

@@ -291,10 +291,10 @@ namespace Newtonsoft.Json.Linq
 #pragma warning restore CS8653 // A default expression introduces a null value for a type parameter.
                     }
 
-                    targetType = Nullable.GetUnderlyingType(targetType);
+                    targetType = Nullable.GetUnderlyingType(targetType)!;
                 }
 
-                return (U)System.Convert.ChangeType(value.Value, targetType, CultureInfo.InvariantCulture);
+                return (U?)System.Convert.ChangeType(value.Value, targetType, CultureInfo.InvariantCulture);
             }
         }
 

Src/Newtonsoft.Json/Linq/JConstructor.cs

@@ -202,7 +202,13 @@ namespace Newtonsoft.Json.Linq
 
         internal override int GetDeepHashCode()
         {
-            return (_name?.GetHashCode() ?? 0) ^ ContentsHashCode();
+            int hash;
+#if HAVE_GETHASHCODE_STRING_COMPARISON
+            hash = _name?.GetHashCode(StringComparison.Ordinal) ?? 0;
+#else
+            hash = _name?.GetHashCode() ?? 0;
+#endif
+            return hash ^ ContentsHashCode();
         }
 
         /// <summary>

Src/Newtonsoft.Json/Linq/JContainer.Async.cs

@@ -109,7 +109,7 @@ namespace Newtonsoft.Json.Linq
                         parent = parent.Parent;
                         break;
                     case JsonToken.StartConstructor:
-                        JConstructor constructor = new JConstructor(reader.Value!.ToString());
+                        JConstructor constructor = new JConstructor(reader.Value!.ToString()!);
                         constructor.SetLineInfo(lineInfo, settings);
                         parent.Add(constructor);
                         parent = constructor;

Src/Newtonsoft.Json/Linq/JContainer.cs

@@ -84,7 +84,7 @@ namespace Newtonsoft.Json.Linq
         /// <summary>
         /// Occurs when the items list of the collection has changed, or the collection is reset.
         /// </summary>
-        public event NotifyCollectionChangedEventHandler CollectionChanged
+        public event NotifyCollectionChangedEventHandler? CollectionChanged
         {
             add { _collectionChanged += value; }
             remove { _collectionChanged -= value; }
@@ -839,7 +839,7 @@ namespace Newtonsoft.Json.Linq
                         parent = parent.Parent;
                         break;
                     case JsonToken.StartConstructor:
-                        JConstructor constructor = new JConstructor(r.Value!.ToString());
+                        JConstructor constructor = new JConstructor(r.Value!.ToString()!);
                         constructor.SetLineInfo(lineInfo, settings);
                         parent.Add(constructor);
                         parent = constructor;
@@ -902,7 +902,7 @@ namespace Newtonsoft.Json.Linq
             DuplicatePropertyNameHandling duplicatePropertyNameHandling = settings?.DuplicatePropertyNameHandling ?? DuplicatePropertyNameHandling.Replace;
 
             JObject parentObject = (JObject)parent;
-            string propertyName = r.Value!.ToString();
+            string propertyName = r.Value!.ToString()!;
             JProperty? existingPropertyWithName = parentObject.Property(propertyName, StringComparison.Ordinal);
             if (existingPropertyWithName != null)
             {
@@ -947,10 +947,11 @@ namespace Newtonsoft.Json.Linq
             return string.Empty;
         }
 
-        PropertyDescriptorCollection? ITypedList.GetItemProperties(PropertyDescriptor[] listAccessors)
+        PropertyDescriptorCollection ITypedList.GetItemProperties(PropertyDescriptor[] listAccessors)
         {
             ICustomTypeDescriptor? d = First as ICustomTypeDescriptor;
-            return d?.GetProperties();
+
+            return d?.GetProperties() ?? new PropertyDescriptorCollection(CollectionUtils.ArrayEmpty<PropertyDescriptor>());
         }
 #endif
 
@@ -1006,7 +1007,7 @@ namespace Newtonsoft.Json.Linq
         }
         #endregion
 
-        private JToken? EnsureValue(object value)
+        private JToken? EnsureValue(object? value)
         {
             if (value == null)
             {
@@ -1022,7 +1023,7 @@ namespace Newtonsoft.Json.Linq
         }
 
         #region IList Members
-        int IList.Add(object value)
+        int IList.Add(object? value)
         {
             Add(EnsureValue(value));
             return Count - 1;
@@ -1033,17 +1034,17 @@ namespace Newtonsoft.Json.Linq
             ClearItems();
         }
 
-        bool IList.Contains(object value)
+        bool IList.Contains(object? value)
         {
             return ContainsItem(EnsureValue(value));
         }
 
-        int IList.IndexOf(object value)
+        int IList.IndexOf(object? value)
         {
             return IndexOfItem(EnsureValue(value));
         }
 
-        void IList.Insert(int index, object value)
+        void IList.Insert(int index, object? value)
         {
             InsertItem(index, EnsureValue(value), false);
         }
@@ -1052,7 +1053,7 @@ namespace Newtonsoft.Json.Linq
 
         bool IList.IsReadOnly => false;
 
-        void IList.Remove(object value)
+        void IList.Remove(object? value)
         {
             RemoveItem(EnsureValue(value));
         }
@@ -1062,7 +1063,7 @@ namespace Newtonsoft.Json.Linq
             RemoveItemAt(index);
         }
 
-        object IList.this[int index]
+        object? IList.this[int index]
         {
             get => GetItem(index);
             set => SetItem(index, EnsureValue(value));

Src/Newtonsoft.Json/Linq/JEnumerable.cs

@@ -111,7 +111,7 @@ namespace Newtonsoft.Json.Linq
         /// <returns>
         /// 	<c>true</c> if the specified <see cref="Object"/> is equal to this instance; otherwise, <c>false</c>.
         /// </returns>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj is JEnumerable<T> enumerable)
             {

Src/Newtonsoft.Json/Linq/JObject.Async.cs

@@ -45,7 +45,7 @@ namespace Newtonsoft.Json.Linq
         public override Task WriteToAsync(JsonWriter writer, CancellationToken cancellationToken, params JsonConverter[] converters)
         {
             Task t = writer.WriteStartObjectAsync(cancellationToken);
-            if (!t.IsCompletedSucessfully())
+            if (!t.IsCompletedSuccessfully())
             {
                 return AwaitProperties(t, 0, writer, cancellationToken, converters);
             }
@@ -53,7 +53,7 @@ namespace Newtonsoft.Json.Linq
             for (int i = 0; i < _properties.Count; i++)
             {
                 t = _properties[i].WriteToAsync(writer, cancellationToken, converters);
-                if (!t.IsCompletedSucessfully())
+                if (!t.IsCompletedSuccessfully())
                 {
                     return AwaitProperties(t, i + 1, writer, cancellationToken, converters);
                 }

Src/Newtonsoft.Json/Linq/JObject.cs

@@ -742,7 +742,7 @@ namespace Newtonsoft.Json.Linq
             return ((ICustomTypeDescriptor)this).GetProperties(null);
         }
 
-        PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties(Attribute[] attributes)
+        PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties(Attribute[]? attributes)
         {
             PropertyDescriptor[] propertiesArray = new PropertyDescriptor[Count];
             int i = 0;
@@ -790,7 +790,7 @@ namespace Newtonsoft.Json.Linq
             return null;
         }
 
-        EventDescriptorCollection ICustomTypeDescriptor.GetEvents(Attribute[] attributes)
+        EventDescriptorCollection ICustomTypeDescriptor.GetEvents(Attribute[]? attributes)
         {
             return EventDescriptorCollection.Empty;
         }
@@ -800,7 +800,7 @@ namespace Newtonsoft.Json.Linq
             return EventDescriptorCollection.Empty;
         }
 
-        object? ICustomTypeDescriptor.GetPropertyOwner(PropertyDescriptor pd)
+        object? ICustomTypeDescriptor.GetPropertyOwner(PropertyDescriptor? pd)
         {
             if (pd is JPropertyDescriptor)
             {

Src/Newtonsoft.Json/Linq/JProperty.Async.cs

@@ -44,7 +44,7 @@ namespace Newtonsoft.Json.Linq
         public override Task WriteToAsync(JsonWriter writer, CancellationToken cancellationToken, params JsonConverter[] converters)
         {
             Task task = writer.WritePropertyNameAsync(_name, cancellationToken);
-            if (task.IsCompletedSucessfully())
+            if (task.IsCompletedSuccessfully())
             {
                 return WriteValueAsync(writer, cancellationToken, converters);
             }

Src/Newtonsoft.Json/Linq/JProperty.cs

@@ -353,7 +353,13 @@ namespace Newtonsoft.Json.Linq
 
         internal override int GetDeepHashCode()
         {
-            return _name.GetHashCode() ^ (Value?.GetDeepHashCode() ?? 0);
+            int hash;
+#if HAVE_GETHASHCODE_STRING_COMPARISON
+            hash = _name.GetHashCode(StringComparison.Ordinal);
+#else
+            hash = _name.GetHashCode();
+#endif
+            return hash ^ (Value?.GetDeepHashCode() ?? 0);
         }
 
         /// <summary>

Src/Newtonsoft.Json/Linq/JPropertyDescriptor.cs

@@ -67,7 +67,7 @@ namespace Newtonsoft.Json.Linq
         /// The value of a property for a given component.
         /// </returns>
         /// <param name="component">The component with the property for which to retrieve the value.</param>
-        public override object? GetValue(object component)
+        public override object? GetValue(object? component)
         {
             return (component as JObject)?[Name];
         }
@@ -85,7 +85,7 @@ namespace Newtonsoft.Json.Linq
         /// </summary>
         /// <param name="component">The component with the property value that is to be set.</param>
         /// <param name="value">The new value.</param>
-        public override void SetValue(object component, object value)
+        public override void SetValue(object? component, object? value)
         {
             if (component is JObject o)
             {

Src/Newtonsoft.Json/Linq/JPropertyKeyedCollection.cs

@@ -131,7 +131,7 @@ namespace Newtonsoft.Json.Linq
 
             if (_dictionary != null)
             {
-                return _dictionary.TryGetValue(key, out JToken value) && Remove(value);
+                return _dictionary.TryGetValue(key, out JToken? value) && Remove(value);
             }
 
             return false;
@@ -259,7 +259,7 @@ namespace Newtonsoft.Json.Linq
 
             foreach (KeyValuePair<string, JToken> keyAndProperty in d1)
             {
-                if (!d2.TryGetValue(keyAndProperty.Key, out JToken secondValue))
+                if (!d2.TryGetValue(keyAndProperty.Key, out JToken? secondValue))
                 {
                     return false;
                 }

Src/Newtonsoft.Json/Linq/JToken.cs

@@ -1333,7 +1333,7 @@ namespace Newtonsoft.Json.Linq
 
             if (v.Value is string)
             {
-                return Convert.FromBase64String(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+                return Convert.FromBase64String(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
             }
 #if HAVE_BIG_INTEGER
             if (v.Value is BigInteger integer)
@@ -1368,7 +1368,7 @@ namespace Newtonsoft.Json.Linq
                 return new Guid(bytes);
             }
 
-            return (v.Value is Guid guid) ? guid : new Guid(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+            return (v.Value is Guid guid) ? guid : new Guid(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
         }
 
         /// <summary>
@@ -1399,7 +1399,7 @@ namespace Newtonsoft.Json.Linq
                 return new Guid(bytes);
             }
 
-            return (v.Value is Guid guid) ? guid : new Guid(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+            return (v.Value is Guid guid) ? guid : new Guid(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
         }
 
         /// <summary>
@@ -1415,7 +1415,7 @@ namespace Newtonsoft.Json.Linq
                 throw new ArgumentException("Can not convert {0} to TimeSpan.".FormatWith(CultureInfo.InvariantCulture, GetType(value)));
             }
 
-            return (v.Value is TimeSpan span) ? span : ConvertUtils.ParseTimeSpan(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+            return (v.Value is TimeSpan span) ? span : ConvertUtils.ParseTimeSpan(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
         }
 
         /// <summary>
@@ -1441,7 +1441,7 @@ namespace Newtonsoft.Json.Linq
                 return null;
             }
 
-            return (v.Value is TimeSpan span) ? span : ConvertUtils.ParseTimeSpan(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+            return (v.Value is TimeSpan span) ? span : ConvertUtils.ParseTimeSpan(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
         }
 
         /// <summary>
@@ -1467,7 +1467,7 @@ namespace Newtonsoft.Json.Linq
                 return null;
             }
 
-            return (v.Value is Uri uri) ? uri : new Uri(Convert.ToString(v.Value, CultureInfo.InvariantCulture));
+            return (v.Value is Uri uri) ? uri : new Uri(Convert.ToString(v.Value, CultureInfo.InvariantCulture)!);
         }
 
 #if HAVE_BIG_INTEGER
@@ -1957,15 +1957,15 @@ namespace Newtonsoft.Json.Linq
                         }
                         catch (Exception ex)
                         {
-                            Type enumType = objectType.IsEnum() ? objectType : Nullable.GetUnderlyingType(objectType);
+                            Type enumType = objectType.IsEnum() ? objectType : Nullable.GetUnderlyingType(objectType)!;
                             throw new ArgumentException("Could not convert '{0}' to {1}.".FormatWith(CultureInfo.InvariantCulture, (string?)this, enumType.Name), ex);
                         }
                     }
 
                     if (Type == JTokenType.Integer)
                     {
-                        Type enumType = objectType.IsEnum() ? objectType : Nullable.GetUnderlyingType(objectType);
-                        return Enum.ToObject(enumType, ((JValue)this).Value);
+                        Type enumType = objectType.IsEnum() ? objectType : Nullable.GetUnderlyingType(objectType)!;
+                        return Enum.ToObject(enumType, ((JValue)this).Value!);
                     }
                 }
 

Src/Newtonsoft.Json/Linq/JTokenEqualityComparer.cs

@@ -40,7 +40,7 @@ namespace Newtonsoft.Json.Linq
         /// <returns>
         /// <c>true</c> if the specified objects are equal; otherwise, <c>false</c>.
         /// </returns>
-        public bool Equals(JToken x, JToken y)
+        public bool Equals(JToken? x, JToken? y)
         {
             return JToken.DeepEquals(x, y);
         }

Src/Newtonsoft.Json/Linq/JValue.cs

@@ -307,8 +307,8 @@ namespace Newtonsoft.Json.Linq
                 case JTokenType.Comment:
                 case JTokenType.String:
                 case JTokenType.Raw:
-                    string s1 = Convert.ToString(objA, CultureInfo.InvariantCulture);
-                    string s2 = Convert.ToString(objB, CultureInfo.InvariantCulture);
+                    string? s1 = Convert.ToString(objA, CultureInfo.InvariantCulture);
+                    string? s2 = Convert.ToString(objB, CultureInfo.InvariantCulture);
 
                     return string.CompareOrdinal(s1, s2);
                 case JTokenType.Boolean:
@@ -859,7 +859,7 @@ namespace Newtonsoft.Json.Linq
         /// <returns>
         /// <c>true</c> if the specified <see cref="Object"/> is equal to the current <see cref="Object"/>; otherwise, <c>false</c>.
         /// </returns>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj is JValue v)
             {
@@ -902,7 +902,7 @@ namespace Newtonsoft.Json.Linq
                 return string.Empty;
             }
 
-            return _value.ToString();
+            return _value.ToString()!;
         }
 
         /// <summary>
@@ -924,7 +924,7 @@ namespace Newtonsoft.Json.Linq
         /// <returns>
         /// A <see cref="String"/> that represents this instance.
         /// </returns>
-        public string ToString(IFormatProvider formatProvider)
+        public string ToString(IFormatProvider? formatProvider)
         {
             return ToString(null, formatProvider);
         }
@@ -937,7 +937,7 @@ namespace Newtonsoft.Json.Linq
         /// <returns>
         /// A <see cref="String"/> that represents this instance.
         /// </returns>
-        public string ToString(string? format, IFormatProvider formatProvider)
+        public string ToString(string? format, IFormatProvider? formatProvider)
         {
             if (_value == null)
             {
@@ -950,7 +950,7 @@ namespace Newtonsoft.Json.Linq
             }
             else
             {
-                return _value.ToString();
+                return _value.ToString()!;
             }
         }
 
@@ -1035,7 +1035,7 @@ namespace Newtonsoft.Json.Linq
         }
 #endif
 
-        int IComparable.CompareTo(object obj)
+        int IComparable.CompareTo(object? obj)
         {
             if (obj == null)
             {
@@ -1078,7 +1078,7 @@ namespace Newtonsoft.Json.Linq
         /// <exception cref="ArgumentException">
         /// 	<paramref name="obj"/> is not of the same type as this instance.
         /// </exception>
-        public int CompareTo(JValue obj)
+        public int CompareTo(JValue? obj)
         {
             if (obj == null)
             {
@@ -1108,79 +1108,79 @@ namespace Newtonsoft.Json.Linq
             return TypeCode.Object;
         }
 
-        bool IConvertible.ToBoolean(IFormatProvider provider)
+        bool IConvertible.ToBoolean(IFormatProvider? provider)
         {
             return (bool)this;
         }
 
-        char IConvertible.ToChar(IFormatProvider provider)
+        char IConvertible.ToChar(IFormatProvider? provider)
         {
             return (char)this;
         }
 
-        sbyte IConvertible.ToSByte(IFormatProvider provider)
+        sbyte IConvertible.ToSByte(IFormatProvider? provider)
         {
             return (sbyte)this;
         }
 
-        byte IConvertible.ToByte(IFormatProvider provider)
+        byte IConvertible.ToByte(IFormatProvider? provider)
         {
             return (byte)this;
         }
 
-        short IConvertible.ToInt16(IFormatProvider provider)
+        short IConvertible.ToInt16(IFormatProvider? provider)
         {
             return (short)this;
         }
 
-        ushort IConvertible.ToUInt16(IFormatProvider provider)
+        ushort IConvertible.ToUInt16(IFormatProvider? provider)
         {
             return (ushort)this;
         }
 
-        int IConvertible.ToInt32(IFormatProvider provider)
+        int IConvertible.ToInt32(IFormatProvider? provider)
         {
             return (int)this;
         }
 
-        uint IConvertible.ToUInt32(IFormatProvider provider)
+        uint IConvertible.ToUInt32(IFormatProvider? provider)
         {
             return (uint)this;
         }
 
-        long IConvertible.ToInt64(IFormatProvider provider)
+        long IConvertible.ToInt64(IFormatProvider? provider)
         {
             return (long)this;
         }
 
-        ulong IConvertible.ToUInt64(IFormatProvider provider)
+        ulong IConvertible.ToUInt64(IFormatProvider? provider)
         {
             return (ulong)this;
         }
 
-        float IConvertible.ToSingle(IFormatProvider provider)
+        float IConvertible.ToSingle(IFormatProvider? provider)
         {
             return (float)this;
         }
 
-        double IConvertible.ToDouble(IFormatProvider provider)
+        double IConvertible.ToDouble(IFormatProvider? provider)
         {
             return (double)this;
         }
 
-        decimal IConvertible.ToDecimal(IFormatProvider provider)
+        decimal IConvertible.ToDecimal(IFormatProvider? provider)
         {
             return (decimal)this;
         }
 
-        DateTime IConvertible.ToDateTime(IFormatProvider provider)
+        DateTime IConvertible.ToDateTime(IFormatProvider? provider)
         {
             return (DateTime)this;
         }
 
-        object? IConvertible.ToType(Type conversionType, IFormatProvider provider)
+        object IConvertible.ToType(Type conversionType, IFormatProvider? provider)
         {
-            return ToObject(conversionType);
+            return ToObject(conversionType)!;
         }
 #endif
     }

Src/Newtonsoft.Json/Linq/JsonPath/QueryExpression.cs

@@ -291,7 +291,7 @@ namespace Newtonsoft.Json.Linq.JsonPath
                     break;
                 case JTokenType.Guid:
                 case JTokenType.TimeSpan:
-                    currentValueString = value.Value!.ToString();
+                    currentValueString = value.Value!.ToString()!;
                     break;
                 case JTokenType.Uri:
                     currentValueString = ((Uri)value.Value!).OriginalString;

Src/Newtonsoft.Json/Newtonsoft.Json.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks Condition="'$(LibraryFrameworks)'==''">net45;net40;net35;net20;netstandard1.0;netstandard1.3;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks Condition="'$(LibraryFrameworks)'==''">net6.0;net45;net40;net35;net20;netstandard1.0;netstandard1.3;netstandard2.0</TargetFrameworks>
     <TargetFrameworks Condition="'$(LibraryFrameworks)'!=''">$(LibraryFrameworks)</TargetFrameworks>
     <LangVersion>9.0</LangVersion>
     <!-- version numbers will be updated by build -->
@@ -51,8 +51,12 @@
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="$(MicrosoftCodeAnalysisNetAnalyzersPackageVersion)" PrivateAssets="All" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="$(MicrosoftSourceLinkGitHubPackageVersion)" PrivateAssets="All" />
   </ItemGroup>
+  <PropertyGroup Condition="'$(TargetFramework)'=='net6.0'">
+    <AssemblyTitle>Json.NET .NET 6.0</AssemblyTitle>
+    <DefineConstants>HAVE_ADO_NET;HAVE_APP_DOMAIN;HAVE_ASYNC;HAVE_BIG_INTEGER;HAVE_BINARY_FORMATTER;HAVE_BINARY_SERIALIZATION;HAVE_BINARY_EXCEPTION_SERIALIZATION;HAVE_CHAR_TO_LOWER_WITH_CULTURE;HAVE_CHAR_TO_STRING_WITH_CULTURE;HAVE_COM_ATTRIBUTES;HAVE_COMPONENT_MODEL;HAVE_CONCURRENT_COLLECTIONS;HAVE_COVARIANT_GENERICS;HAVE_DATA_CONTRACTS;HAVE_DATE_TIME_OFFSET;HAVE_DB_NULL_TYPE_CODE;HAVE_DYNAMIC;HAVE_EMPTY_TYPES;HAVE_ENTITY_FRAMEWORK;HAVE_EXPRESSIONS;HAVE_FAST_REVERSE;HAVE_FSHARP_TYPES;HAVE_FULL_REFLECTION;HAVE_GUID_TRY_PARSE;HAVE_HASH_SET;HAVE_ICLONEABLE;HAVE_ICONVERTIBLE;HAVE_IGNORE_DATA_MEMBER_ATTRIBUTE;HAVE_INOTIFY_COLLECTION_CHANGED;HAVE_INOTIFY_PROPERTY_CHANGING;HAVE_ISET;HAVE_LINQ;HAVE_MEMORY_BARRIER;HAVE_METHOD_IMPL_ATTRIBUTE;HAVE_NON_SERIALIZED_ATTRIBUTE;HAVE_READ_ONLY_COLLECTIONS;HAVE_REFLECTION_EMIT;HAVE_REGEX_TIMEOUTS;HAVE_SECURITY_SAFE_CRITICAL_ATTRIBUTE;HAVE_SERIALIZATION_BINDER_BIND_TO_NAME;HAVE_STREAM_READER_WRITER_CLOSE;HAVE_STRING_JOIN_WITH_ENUMERABLE;HAVE_TIME_SPAN_PARSE_WITH_CULTURE;HAVE_TIME_SPAN_TO_STRING_WITH_CULTURE;HAVE_TIME_ZONE_INFO;HAVE_TRACE_WRITER;HAVE_TYPE_DESCRIPTOR;HAVE_UNICODE_SURROGATE_DETECTION;HAVE_VARIANT_TYPE_PARAMETERS;HAVE_VERSION_TRY_PARSE;HAVE_XLINQ;HAVE_XML_DOCUMENT;HAVE_XML_DOCUMENT_TYPE;HAVE_CONCURRENT_DICTIONARY;HAVE_INDEXOF_STRING_COMPARISON;HAVE_REPLACE_STRING_COMPARISON;HAVE_REPLACE_STRING_COMPARISON;HAVE_GETHASHCODE_STRING_COMPARISON;HAVE_NULLABLE_ATTRIBUTES;HAVE_DYNAMIC_CODE_COMPILED;HAS_ARRAY_EMPTY;$(AdditionalConstants)</DefineConstants>
+  </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)'=='net45'">
-    <AssemblyTitle>Json.NET</AssemblyTitle>
+    <AssemblyTitle>Json.NET .NET 4.5</AssemblyTitle>
     <DefineConstants>HAVE_ADO_NET;HAVE_APP_DOMAIN;HAVE_ASYNC;HAVE_BIG_INTEGER;HAVE_BINARY_FORMATTER;HAVE_BINARY_SERIALIZATION;HAVE_BINARY_EXCEPTION_SERIALIZATION;HAVE_CAS;HAVE_CHAR_TO_LOWER_WITH_CULTURE;HAVE_CHAR_TO_STRING_WITH_CULTURE;HAVE_COM_ATTRIBUTES;HAVE_COMPONENT_MODEL;HAVE_CONCURRENT_COLLECTIONS;HAVE_COVARIANT_GENERICS;HAVE_DATA_CONTRACTS;HAVE_DATE_TIME_OFFSET;HAVE_DB_NULL_TYPE_CODE;HAVE_DYNAMIC;HAVE_EMPTY_TYPES;HAVE_ENTITY_FRAMEWORK;HAVE_EXPRESSIONS;HAVE_FAST_REVERSE;HAVE_FSHARP_TYPES;HAVE_FULL_REFLECTION;HAVE_GUID_TRY_PARSE;HAVE_HASH_SET;HAVE_ICLONEABLE;HAVE_ICONVERTIBLE;HAVE_IGNORE_DATA_MEMBER_ATTRIBUTE;HAVE_INOTIFY_COLLECTION_CHANGED;HAVE_INOTIFY_PROPERTY_CHANGING;HAVE_ISET;HAVE_LINQ;HAVE_MEMORY_BARRIER;HAVE_METHOD_IMPL_ATTRIBUTE;HAVE_NON_SERIALIZED_ATTRIBUTE;HAVE_READ_ONLY_COLLECTIONS;HAVE_REFLECTION_EMIT;HAVE_REGEX_TIMEOUTS;HAVE_SECURITY_SAFE_CRITICAL_ATTRIBUTE;HAVE_SERIALIZATION_BINDER_BIND_TO_NAME;HAVE_STREAM_READER_WRITER_CLOSE;HAVE_STRING_JOIN_WITH_ENUMERABLE;HAVE_TIME_SPAN_PARSE_WITH_CULTURE;HAVE_TIME_SPAN_TO_STRING_WITH_CULTURE;HAVE_TIME_ZONE_INFO;HAVE_TRACE_WRITER;HAVE_TYPE_DESCRIPTOR;HAVE_UNICODE_SURROGATE_DETECTION;HAVE_VARIANT_TYPE_PARAMETERS;HAVE_VERSION_TRY_PARSE;HAVE_XLINQ;HAVE_XML_DOCUMENT;HAVE_XML_DOCUMENT_TYPE;HAVE_CONCURRENT_DICTIONARY;$(AdditionalConstants)</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)'=='net40'">

Src/Newtonsoft.Json/Schema/JsonSchemaBuilder.cs

@@ -89,7 +89,10 @@ namespace Newtonsoft.Json.Schema
 
         private string UnescapeReference(string reference)
         {
-            return Uri.UnescapeDataString(reference).Replace("~1", "/").Replace("~0", "~");
+            string unescapedReference = Uri.UnescapeDataString(reference);
+            unescapedReference = StringUtils.Replace(unescapedReference, "~1", "/");
+            unescapedReference = StringUtils.Replace(unescapedReference, "~0", "~");
+            return unescapedReference;
         }
 
         private JsonSchema ResolveReferences(JsonSchema schema)
@@ -220,7 +223,11 @@ namespace Newtonsoft.Json.Schema
                 return deferredSchema;
             }
 
-            string location = token.Path.Replace(".", "/").Replace("[", "/").Replace("]", string.Empty);
+            string location = token.Path;
+            location = StringUtils.Replace(location, ".", "/");
+            location = StringUtils.Replace(location, "[", "/");
+            location = StringUtils.Replace(location, "]", string.Empty);
+
             if (!StringUtils.IsNullOrEmpty(location))
             {
                 location = "/" + location;

Src/Newtonsoft.Json/Serialization/CamelCasePropertyNamesContractResolver.cs

@@ -66,7 +66,7 @@ namespace Newtonsoft.Json.Serialization
             // for backwards compadibility the CamelCasePropertyNamesContractResolver shares contracts between instances
             StructMultiKey<Type, Type> key = new StructMultiKey<Type, Type>(GetType(), type);
             Dictionary<StructMultiKey<Type, Type>, JsonContract>? cache = _contractCache;
-            if (cache == null || !cache.TryGetValue(key, out JsonContract contract))
+            if (cache == null || !cache.TryGetValue(key, out JsonContract? contract))
             {
                 contract = CreateContract(type);
 

Src/Newtonsoft.Json/Serialization/DefaultContractResolver.cs

@@ -418,7 +418,7 @@ namespace Newtonsoft.Json.Serialization
                 }
             }
 
-            MemberInfo extensionDataMember = GetExtensionDataMemberForType(contract.NonNullableUnderlyingType);
+            MemberInfo? extensionDataMember = GetExtensionDataMemberForType(contract.NonNullableUnderlyingType);
             if (extensionDataMember != null)
             {
                 SetExtensionDataDelegates(contract, extensionDataMember);
@@ -439,7 +439,7 @@ namespace Newtonsoft.Json.Serialization
             throw new JsonSerializationException("Unable to serialize instance of '{0}'.".FormatWith(CultureInfo.InvariantCulture, o.GetType()));
         }
 
-        private MemberInfo GetExtensionDataMemberForType(Type type)
+        private MemberInfo? GetExtensionDataMemberForType(Type type)
         {
             IEnumerable<MemberInfo> members = GetClassHierarchyForType(type).SelectMany(baseType =>
             {
@@ -450,7 +450,7 @@ namespace Newtonsoft.Json.Serialization
                 return m;
             });
 
-            MemberInfo extensionDataMember = members.LastOrDefault(m =>
+            MemberInfo? extensionDataMember = members.LastOrDefault(m =>
             {
                 MemberTypes memberType = m.MemberType();
                 if (memberType != MemberTypes.Property && memberType != MemberTypes.Field)
@@ -466,7 +466,7 @@ namespace Newtonsoft.Json.Serialization
 
                 if (!ReflectionUtils.CanReadMemberValue(m, true))
                 {
-                    throw new JsonException("Invalid extension data attribute on '{0}'. Member '{1}' must have a getter.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(m.DeclaringType), m.Name));
+                    throw new JsonException("Invalid extension data attribute on '{0}'. Member '{1}' must have a getter.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(m.DeclaringType!), m.Name));
                 }
 
                 Type t = ReflectionUtils.GetMemberUnderlyingType(m);
@@ -482,7 +482,7 @@ namespace Newtonsoft.Json.Serialization
                     }
                 }
 
-                throw new JsonException("Invalid extension data attribute on '{0}'. Member '{1}' type must implement IDictionary<string, JToken>.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(m.DeclaringType), m.Name));
+                throw new JsonException("Invalid extension data attribute on '{0}'. Member '{1}' type must implement IDictionary<string, JToken>.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(m.DeclaringType!), m.Name));
             });
 
             return extensionDataMember;
@@ -640,7 +640,7 @@ namespace Newtonsoft.Json.Serialization
                     {
                         foreach (ParameterInfo parameterInfo in parameters)
                         {
-                            JsonProperty? memberProperty = MatchProperty(memberProperties, parameterInfo.Name, parameterInfo.ParameterType);
+                            JsonProperty? memberProperty = MatchProperty(memberProperties, parameterInfo.Name!, parameterInfo.ParameterType);
                             if (memberProperty == null || memberProperty.Writable)
                             {
                                 return null;
@@ -688,7 +688,7 @@ namespace Newtonsoft.Json.Serialization
         {
             ParameterInfo[] constructorParameters = constructor.GetParameters();
 
-            JsonPropertyCollection parameterCollection = new JsonPropertyCollection(constructor.DeclaringType);
+            JsonPropertyCollection parameterCollection = new JsonPropertyCollection(constructor.DeclaringType!);
 
             foreach (ParameterInfo parameterInfo in constructorParameters)
             {
@@ -746,7 +746,7 @@ namespace Newtonsoft.Json.Serialization
             property.PropertyType = parameterInfo.ParameterType;
             property.AttributeProvider = new ReflectionAttributeProvider(parameterInfo);
 
-            SetPropertySettingsFromAttributes(property, parameterInfo, parameterInfo.Name, parameterInfo.Member.DeclaringType, MemberSerialization.OptOut, out _);
+            SetPropertySettingsFromAttributes(property, parameterInfo, parameterInfo.Name!, parameterInfo.Member.DeclaringType!, MemberSerialization.OptOut, out _);
 
             property.Readable = false;
             property.Writable = true;
@@ -989,7 +989,7 @@ namespace Newtonsoft.Json.Serialization
         {
             List<Type> ret = new List<Type>();
 
-            Type current = type;
+            Type? current = type;
             while (current != null && current != typeof(object))
             {
                 ret.Add(current);
@@ -1127,7 +1127,7 @@ namespace Newtonsoft.Json.Serialization
 
             if (contract.IsInstantiable)
             {
-                ConstructorInfo constructorInfo = contract.NonNullableUnderlyingType.GetConstructor(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, new[] {typeof(SerializationInfo), typeof(StreamingContext)}, null);
+                ConstructorInfo? constructorInfo = contract.NonNullableUnderlyingType.GetConstructor(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, new[] {typeof(SerializationInfo), typeof(StreamingContext)}, null);
                 if (constructorInfo != null)
                 {
                     ObjectConstructor<object> creator = JsonTypeReflector.ReflectionDelegateFactory.CreateParameterizedConstructor(constructorInfo);
@@ -1304,36 +1304,36 @@ namespace Newtonsoft.Json.Serialization
 
             if (currentCallback != null)
             {
-                throw new JsonException("Invalid attribute. Both '{0}' and '{1}' in type '{2}' have '{3}'.".FormatWith(CultureInfo.InvariantCulture, method, currentCallback, GetClrTypeFullName(method.DeclaringType), attributeType));
+                throw new JsonException("Invalid attribute. Both '{0}' and '{1}' in type '{2}' have '{3}'.".FormatWith(CultureInfo.InvariantCulture, method, currentCallback, GetClrTypeFullName(method.DeclaringType!), attributeType));
             }
 
             if (prevAttributeType != null)
             {
-                throw new JsonException("Invalid Callback. Method '{3}' in type '{2}' has both '{0}' and '{1}'.".FormatWith(CultureInfo.InvariantCulture, prevAttributeType, attributeType, GetClrTypeFullName(method.DeclaringType), method));
+                throw new JsonException("Invalid Callback. Method '{3}' in type '{2}' has both '{0}' and '{1}'.".FormatWith(CultureInfo.InvariantCulture, prevAttributeType, attributeType, GetClrTypeFullName(method.DeclaringType!), method));
             }
 
             if (method.IsVirtual)
             {
-                throw new JsonException("Virtual Method '{0}' of type '{1}' cannot be marked with '{2}' attribute.".FormatWith(CultureInfo.InvariantCulture, method, GetClrTypeFullName(method.DeclaringType), attributeType));
+                throw new JsonException("Virtual Method '{0}' of type '{1}' cannot be marked with '{2}' attribute.".FormatWith(CultureInfo.InvariantCulture, method, GetClrTypeFullName(method.DeclaringType!), attributeType));
             }
 
             if (method.ReturnType != typeof(void))
             {
-                throw new JsonException("Serialization Callback '{1}' in type '{0}' must return void.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType), method));
+                throw new JsonException("Serialization Callback '{1}' in type '{0}' must return void.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType!), method));
             }
 
             if (attributeType == typeof(OnErrorAttribute))
             {
                 if (parameters == null || parameters.Length != 2 || parameters[0].ParameterType != typeof(StreamingContext) || parameters[1].ParameterType != typeof(ErrorContext))
                 {
-                    throw new JsonException("Serialization Error Callback '{1}' in type '{0}' must have two parameters of type '{2}' and '{3}'.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType), method, typeof(StreamingContext), typeof(ErrorContext)));
+                    throw new JsonException("Serialization Error Callback '{1}' in type '{0}' must have two parameters of type '{2}' and '{3}'.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType!), method, typeof(StreamingContext), typeof(ErrorContext)));
                 }
             }
             else
             {
                 if (parameters == null || parameters.Length != 1 || parameters[0].ParameterType != typeof(StreamingContext))
                 {
-                    throw new JsonException("Serialization Callback '{1}' in type '{0}' must have a single parameter of type '{2}'.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType), method, typeof(StreamingContext)));
+                    throw new JsonException("Serialization Callback '{1}' in type '{0}' must have a single parameter of type '{2}'.".FormatWith(CultureInfo.InvariantCulture, GetClrTypeFullName(method.DeclaringType!), method, typeof(StreamingContext)));
                 }
             }
 
@@ -1346,7 +1346,7 @@ namespace Newtonsoft.Json.Serialization
         {
             if (type.IsGenericTypeDefinition() || !type.ContainsGenericParameters())
             {
-                return type.FullName;
+                return type.FullName!;
             }
 
             return "{0}.{1}".FormatWith(CultureInfo.InvariantCulture, type.Namespace, type.Name);
@@ -1437,7 +1437,7 @@ namespace Newtonsoft.Json.Serialization
             property.ValueProvider = CreateMemberValueProvider(member);
             property.AttributeProvider = new ReflectionAttributeProvider(member);
 
-            SetPropertySettingsFromAttributes(property, member, member.Name, member.DeclaringType, memberSerialization, out bool allowNonPublicAccess);
+            SetPropertySettingsFromAttributes(property, member, member.Name, member.DeclaringType!, memberSerialization, out bool allowNonPublicAccess);
 
             if (memberSerialization != MemberSerialization.Fields)
             {
@@ -1635,7 +1635,7 @@ namespace Newtonsoft.Json.Serialization
 
         private Predicate<object>? CreateShouldSerializeTest(MemberInfo member)
         {
-            MethodInfo shouldSerializeMethod = member.DeclaringType.GetMethod(JsonTypeReflector.ShouldSerializePrefix + member.Name, ReflectionUtils.EmptyTypes);
+            MethodInfo? shouldSerializeMethod = member.DeclaringType!.GetMethod(JsonTypeReflector.ShouldSerializePrefix + member.Name, ReflectionUtils.EmptyTypes);
 
             if (shouldSerializeMethod == null || shouldSerializeMethod.ReturnType != typeof(bool))
             {
@@ -1650,7 +1650,7 @@ namespace Newtonsoft.Json.Serialization
 
         private void SetIsSpecifiedActions(JsonProperty property, MemberInfo member, bool allowNonPublicAccess)
         {
-            MemberInfo? specifiedMember = member.DeclaringType.GetProperty(member.Name + JsonTypeReflector.SpecifiedPostfix, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
+            MemberInfo? specifiedMember = member.DeclaringType!.GetProperty(member.Name + JsonTypeReflector.SpecifiedPostfix, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
             if (specifiedMember == null)
             {
                 specifiedMember = member.DeclaringType.GetField(member.Name + JsonTypeReflector.SpecifiedPostfix, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

Src/Newtonsoft.Json/Serialization/DefaultReferenceResolver.cs

@@ -52,15 +52,15 @@ namespace Newtonsoft.Json.Serialization
 
         public object ResolveReference(object context, string reference)
         {
-            GetMappings(context).TryGetByFirst(reference, out object value);
-            return value;
+            GetMappings(context).TryGetByFirst(reference, out object? value);
+            return value!;
         }
 
         public string GetReference(object context, object value)
         {
             BidirectionalDictionary<string, object> mappings = GetMappings(context);
 
-            if (!mappings.TryGetBySecond(value, out string reference))
+            if (!mappings.TryGetBySecond(value, out string? reference))
             {
                 _referenceCount++;
                 reference = _referenceCount.ToString(CultureInfo.InvariantCulture);

Src/Newtonsoft.Json/Serialization/DefaultSerializationBinder.cs

@@ -60,7 +60,7 @@ namespace Newtonsoft.Json.Serialization
 
             if (assemblyName != null)
             {
-                Assembly assembly;
+                Assembly? assembly;
 
 #if !(DOTNET || PORTABLE40 || PORTABLE)
                 // look, I don't like using obsolete methods as much as you do but this is the only way
@@ -101,7 +101,7 @@ namespace Newtonsoft.Json.Serialization
                 {
                     // if generic type, try manually parsing the type arguments for the case of dynamically loaded assemblies
                     // example generic typeName format: System.Collections.Generic.Dictionary`2[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]
-                    if (typeName.IndexOf('`') >= 0)
+                    if (StringUtils.IndexOf(typeName, '`') >= 0)
                     {
                         try
                         {
@@ -123,18 +123,18 @@ namespace Newtonsoft.Json.Serialization
             }
             else
             {
-                return Type.GetType(typeName);
+                return Type.GetType(typeName)!;
             }
         }
 
         private Type? GetGenericTypeFromTypeName(string typeName, Assembly assembly)
         {
             Type? type = null;
-            int openBracketIndex = typeName.IndexOf('[');
+            int openBracketIndex = StringUtils.IndexOf(typeName, '[');
             if (openBracketIndex >= 0)
             {
                 string genericTypeDefName = typeName.Substring(0, openBracketIndex);
-                Type genericTypeDef = assembly.GetType(genericTypeDefName);
+                Type? genericTypeDef = assembly.GetType(genericTypeDefName);
                 if (genericTypeDef != null)
                 {
                     List<Type> genericTypeArguments = new List<Type>();

Src/Newtonsoft.Json/Serialization/JsonArrayContract.cs

@@ -127,7 +127,7 @@ namespace Newtonsoft.Json.Serialization
             Type? tempCollectionType;
             if (IsArray)
             {
-                CollectionItemType = ReflectionUtils.GetCollectionItemType(UnderlyingType);
+                CollectionItemType = ReflectionUtils.GetCollectionItemType(UnderlyingType)!;
                 IsReadOnlyOrFixedSize = true;
                 _genericCollectionDefinitionType = typeof(List<>).MakeGenericType(CollectionItemType);
 
@@ -274,6 +274,7 @@ namespace Newtonsoft.Json.Serialization
             if (_genericWrapperCreator == null)
             {
                 MiscellaneousUtils.Assert(_genericCollectionDefinitionType != null);
+                MiscellaneousUtils.Assert(CollectionItemType != null);
 
                 _genericWrapperType = typeof(CollectionWrapper<>).MakeGenericType(CollectionItemType);
 
@@ -289,7 +290,7 @@ namespace Newtonsoft.Json.Serialization
                     constructorArgument = _genericCollectionDefinitionType;
                 }
 
-                ConstructorInfo genericWrapperConstructor = _genericWrapperType.GetConstructor(new[] { constructorArgument });
+                ConstructorInfo genericWrapperConstructor = _genericWrapperType.GetConstructor(new[] { constructorArgument })!;
                 _genericWrapperCreator = JsonTypeReflector.ReflectionDelegateFactory.CreateParameterizedConstructor(genericWrapperConstructor);
             }
 

Src/Newtonsoft.Json/Serialization/JsonContract.cs

@@ -248,7 +248,7 @@ namespace Newtonsoft.Json.Serialization
 
             IsNullable = ReflectionUtils.IsNullable(underlyingType);
              
-            NonNullableUnderlyingType = (IsNullable && ReflectionUtils.IsNullableType(underlyingType)) ? Nullable.GetUnderlyingType(underlyingType) : underlyingType;
+            NonNullableUnderlyingType = (IsNullable && ReflectionUtils.IsNullableType(underlyingType)) ? Nullable.GetUnderlyingType(underlyingType)! : underlyingType;
 
             _createdType = CreatedType = NonNullableUnderlyingType;
 

Src/Newtonsoft.Json/Serialization/JsonDictionaryContract.cs

@@ -223,9 +223,9 @@ namespace Newtonsoft.Json.Serialization
         {
             if (_genericWrapperCreator == null)
             {
-                _genericWrapperType = typeof(DictionaryWrapper<,>).MakeGenericType(DictionaryKeyType, DictionaryValueType);
+                _genericWrapperType = typeof(DictionaryWrapper<,>).MakeGenericType(DictionaryKeyType!, DictionaryValueType!);
 
-                ConstructorInfo genericWrapperConstructor = _genericWrapperType.GetConstructor(new[] { _genericCollectionDefinitionType! });
+                ConstructorInfo genericWrapperConstructor = _genericWrapperType.GetConstructor(new[] { _genericCollectionDefinitionType! })!;
                 _genericWrapperCreator = JsonTypeReflector.ReflectionDelegateFactory.CreateParameterizedConstructor(genericWrapperConstructor);
             }
 

Src/Newtonsoft.Json/Serialization/JsonFormatterConverter.cs

@@ -53,10 +53,10 @@ namespace Newtonsoft.Json.Serialization
             ValidationUtils.ArgumentNotNull(value, nameof(value));
 
             JValue v = (JValue)value;
-            return (T)System.Convert.ChangeType(v.Value, typeof(T), CultureInfo.InvariantCulture);
+            return (T)System.Convert.ChangeType(v.Value, typeof(T), CultureInfo.InvariantCulture)!;
         }
 
-        public object? Convert(object value, Type type)
+        public object Convert(object value, Type type)
         {
             ValidationUtils.ArgumentNotNull(value, nameof(value));
 
@@ -65,7 +65,7 @@ namespace Newtonsoft.Json.Serialization
                 throw new ArgumentException("Value is not a JToken.", nameof(value));
             }
 
-            return _reader.CreateISerializableItem(token, type, _contract, _member);
+            return _reader.CreateISerializableItem(token, type, _contract, _member)!;
         }
 
         public object Convert(object value, TypeCode typeCode)
@@ -74,7 +74,7 @@ namespace Newtonsoft.Json.Serialization
 
             object? resolvedValue = (value is JValue v) ? v.Value : value;
 
-            return System.Convert.ChangeType(resolvedValue, typeCode, CultureInfo.InvariantCulture);
+            return System.Convert.ChangeType(resolvedValue, typeCode, CultureInfo.InvariantCulture)!;
         }
 
         public bool ToBoolean(object value)

Src/Newtonsoft.Json/Serialization/JsonPropertyCollection.cs

@@ -145,7 +145,7 @@ namespace Newtonsoft.Json.Serialization
             return property;
         }
 
-        private bool TryGetValue(string key, [NotNullWhen(true)]out JsonProperty? item)
+        private bool TryGetProperty(string key, [NotNullWhen(true)]out JsonProperty? item)
         {
             if (Dictionary == null)
             {
@@ -167,7 +167,7 @@ namespace Newtonsoft.Json.Serialization
             // KeyedCollection has an ordinal comparer
             if (comparisonType == StringComparison.Ordinal)
             {
-                if (TryGetValue(propertyName, out JsonProperty? property))
+                if (TryGetProperty(propertyName, out JsonProperty? property))
                 {
                     return property;
                 }

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalBase.cs

@@ -35,7 +35,7 @@ namespace Newtonsoft.Json.Serialization
     {
         private class ReferenceEqualsEqualityComparer : IEqualityComparer<object>
         {
-            bool IEqualityComparer<object>.Equals(object x, object y)
+            bool IEqualityComparer<object>.Equals(object? x, object? y)
             {
                 return ReferenceEquals(x, y);
             }

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs

@@ -332,7 +332,7 @@ namespace Newtonsoft.Json.Serialization
 
                         return EnsureType(reader, s, CultureInfo.InvariantCulture, contract, objectType);
                     case JsonToken.StartConstructor:
-                        string constructorName = reader.Value!.ToString();
+                        string constructorName = reader.Value!.ToString()!;
 
                         return EnsureType(reader, constructorName, CultureInfo.InvariantCulture, contract, objectType);
                     case JsonToken.Null:
@@ -692,7 +692,7 @@ namespace Newtonsoft.Json.Serialization
 
             if (reader.TokenType == JsonToken.PropertyName)
             {
-                string propertyName = reader.Value!.ToString();
+                string propertyName = reader.Value!.ToString()!;
 
                 if (propertyName.Length > 0 && propertyName[0] == '$')
                 {
@@ -702,7 +702,7 @@ namespace Newtonsoft.Json.Serialization
 
                     do
                     {
-                        propertyName = reader.Value!.ToString();
+                        propertyName = reader.Value!.ToString()!;
 
                         if (string.Equals(propertyName, JsonTypeReflector.RefPropertyName, StringComparison.Ordinal))
                         {
@@ -740,7 +740,7 @@ namespace Newtonsoft.Json.Serialization
                         else if (string.Equals(propertyName, JsonTypeReflector.TypePropertyName, StringComparison.Ordinal))
                         {
                             reader.ReadAndAssert();
-                            string qualifiedTypeName = reader.Value!.ToString();
+                            string qualifiedTypeName = reader.Value!.ToString()!;
 
                             ResolveTypeName(reader, ref objectType, ref contract, member, containerContract, containerMember, qualifiedTypeName);
 
@@ -898,7 +898,7 @@ namespace Newtonsoft.Json.Serialization
                     }
                     else if (arrayContract.IsArray)
                     {
-                        Array a = Array.CreateInstance(arrayContract.CollectionItemType, list.Count);
+                        Array a = Array.CreateInstance(arrayContract.CollectionItemType!, list.Count);
                         list.CopyTo(a, 0);
                         list = a;
                     }
@@ -975,7 +975,7 @@ namespace Newtonsoft.Json.Serialization
                             }
                             if (ConvertUtils.IsInteger(primitiveContract.TypeCode))
                             {
-                                return Enum.ToObject(contract.NonNullableUnderlyingType, value);
+                                return Enum.ToObject(contract.NonNullableUnderlyingType, value!);
                             }
                         }
                         else if (contract.NonNullableUnderlyingType == typeof(DateTime))
@@ -1384,7 +1384,7 @@ namespace Newtonsoft.Json.Serialization
                 {
                     case JsonToken.PropertyName:
                         object keyValue = reader.Value!;
-                        if (CheckPropertyName(reader, keyValue.ToString()))
+                        if (CheckPropertyName(reader, keyValue.ToString()!))
                         {
                             continue;
                         }
@@ -1399,7 +1399,7 @@ namespace Newtonsoft.Json.Serialization
                                     case PrimitiveTypeCode.DateTime:
                                     case PrimitiveTypeCode.DateTimeNullable:
                                     {
-                                        keyValue = DateTimeUtils.TryParseDateTime(keyValue.ToString(), reader.DateTimeZoneHandling, reader.DateFormatString, reader.Culture, out DateTime dt)
+                                        keyValue = DateTimeUtils.TryParseDateTime(keyValue.ToString()!, reader.DateTimeZoneHandling, reader.DateFormatString, reader.Culture, out DateTime dt)
                                             ? dt
                                             : EnsureType(reader, keyValue, CultureInfo.InvariantCulture, contract.KeyContract, contract.DictionaryKeyType)!;
                                         break;
@@ -1408,7 +1408,7 @@ namespace Newtonsoft.Json.Serialization
                                     case PrimitiveTypeCode.DateTimeOffset:
                                     case PrimitiveTypeCode.DateTimeOffsetNullable:
                                     {
-                                        keyValue = DateTimeUtils.TryParseDateTimeOffset(keyValue.ToString(), reader.DateFormatString, reader.Culture, out DateTimeOffset dt)
+                                        keyValue = DateTimeUtils.TryParseDateTimeOffset(keyValue.ToString()!, reader.DateFormatString, reader.Culture, out DateTimeOffset dt)
                                             ? dt
                                             : EnsureType(reader, keyValue, CultureInfo.InvariantCulture, contract.KeyContract, contract.DictionaryKeyType)!;
                                         break;
@@ -1416,7 +1416,7 @@ namespace Newtonsoft.Json.Serialization
 #endif
                                     default:
                                         keyValue = contract.KeyContract != null && contract.KeyContract.IsEnum
-                                            ? EnumUtils.ParseEnum(contract.KeyContract.NonNullableUnderlyingType, (Serializer._contractResolver as DefaultContractResolver)?.NamingStrategy, keyValue.ToString(), false)
+                                            ? EnumUtils.ParseEnum(contract.KeyContract.NonNullableUnderlyingType, (Serializer._contractResolver as DefaultContractResolver)?.NamingStrategy, keyValue.ToString()!, false)
                                             : EnsureType(reader, keyValue, CultureInfo.InvariantCulture, contract.KeyContract, contract.DictionaryKeyType)!;
                                         break;
                                 }
@@ -1752,7 +1752,7 @@ namespace Newtonsoft.Json.Serialization
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string memberName = reader.Value!.ToString();
+                        string memberName = reader.Value!.ToString()!;
                         if (!reader.Read())
                         {
                             throw JsonSerializationException.Create(reader, "Unexpected end when setting {0}'s value.".FormatWith(CultureInfo.InvariantCulture, memberName));
@@ -1855,7 +1855,7 @@ namespace Newtonsoft.Json.Serialization
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string memberName = reader.Value!.ToString();
+                        string memberName = reader.Value!.ToString()!;
 
                         try
                         {
@@ -2207,7 +2207,7 @@ namespace Newtonsoft.Json.Serialization
                 switch (reader.TokenType)
                 {
                     case JsonToken.PropertyName:
-                        string memberName = reader.Value!.ToString();
+                        string memberName = reader.Value!.ToString()!;
 
                         CreatorPropertyContext creatorPropertyContext = new CreatorPropertyContext(memberName)
                         {
@@ -2356,7 +2356,7 @@ namespace Newtonsoft.Json.Serialization
                 {
                     case JsonToken.PropertyName:
                     {
-                        string propertyName = reader.Value!.ToString();
+                        string propertyName = reader.Value!.ToString()!;
 
                         if (CheckPropertyName(reader, propertyName))
                         {

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs

@@ -399,7 +399,7 @@ namespace Newtonsoft.Json.Serialization
 #if HAVE_TYPE_DESCRIPTOR
             if (JsonTypeReflector.CanTypeDescriptorConvertString(type, out TypeConverter converter))
             {
-                s = converter.ConvertToInvariantString(value);
+                s = converter.ConvertToInvariantString(value)!;
                 return true;
             }
 #endif
@@ -414,7 +414,7 @@ namespace Newtonsoft.Json.Serialization
 
             if (value is Type t)
             {
-                s = t.AssemblyQualifiedName;
+                s = t.AssemblyQualifiedName!;
                 return true;
             }
 
@@ -778,7 +778,7 @@ namespace Newtonsoft.Json.Serialization
 
                 if (isTopLevel)
                 {
-                    object value = values.GetValue(newIndices);
+                    object value = values.GetValue(newIndices)!;
 
                     try
                     {
@@ -879,7 +879,7 @@ namespace Newtonsoft.Json.Serialization
                 if (ShouldWriteReference(serializationEntry.Value, null, valueContract, contract, member))
                 {
                     writer.WritePropertyName(serializationEntry.Name);
-                    WriteReference(writer, serializationEntry.Value);
+                    WriteReference(writer, serializationEntry.Value!);
                 }
                 else if (CheckForCircularReference(writer, serializationEntry.Value, null, valueContract, contract, member))
                 {
@@ -1176,7 +1176,7 @@ namespace Newtonsoft.Json.Serialization
                             return enumName;
                         }
 
-                        return Convert.ToString(name, CultureInfo.InvariantCulture);
+                        return Convert.ToString(name, CultureInfo.InvariantCulture)!;
                     }
                 }
             }
@@ -1188,7 +1188,7 @@ namespace Newtonsoft.Json.Serialization
             else
             {
                 escape = true;
-                return name.ToString();
+                return name.ToString()!;
             }
         }
 

Src/Newtonsoft.Json/Serialization/JsonTypeReflector.cs

@@ -33,6 +33,7 @@ using System.Security;
 using System.Security.Permissions;
 #endif
 using Newtonsoft.Json.Utilities;
+using System.Runtime.CompilerServices;
 #if !HAVE_LINQ
 using Newtonsoft.Json.Utilities.LinqBridge;
 #else
@@ -99,7 +100,7 @@ namespace Newtonsoft.Json.Serialization
         public static DataContractAttribute? GetDataContractAttribute(Type type)
         {
             // DataContractAttribute does not have inheritance
-            Type currentType = type;
+            Type? currentType = type;
 
             while (currentType != null)
             {
@@ -132,11 +133,11 @@ namespace Newtonsoft.Json.Serialization
             {
                 if (propertyInfo.IsVirtual())
                 {
-                    Type currentType = propertyInfo.DeclaringType;
+                    Type? currentType = propertyInfo.DeclaringType;
 
                     while (result == null && currentType != null)
                     {
-                        PropertyInfo baseProperty = (PropertyInfo)ReflectionUtils.GetMemberInfoFromType(currentType, propertyInfo);
+                        PropertyInfo? baseProperty = (PropertyInfo?)ReflectionUtils.GetMemberInfoFromType(currentType, propertyInfo);
                         if (baseProperty != null && baseProperty.IsVirtual())
                         {
                             result = CachedAttributeGetter<DataMemberAttribute>.GetAttribute(baseProperty);
@@ -248,7 +249,7 @@ namespace Newtonsoft.Json.Serialization
 
                             return param.GetType();
                         }).ToArray();
-                        ConstructorInfo parameterizedConstructorInfo = type.GetConstructor(paramTypes);
+                        ConstructorInfo? parameterizedConstructorInfo = type.GetConstructor(paramTypes);
 
                         if (parameterizedConstructorInfo != null)
                         {
@@ -347,10 +348,10 @@ namespace Newtonsoft.Json.Serialization
             T? attribute;
 
 #if !(NET20 || DOTNET)
-            Type? metadataType = GetAssociatedMetadataType(memberInfo.DeclaringType);
+            Type? metadataType = GetAssociatedMetadataType(memberInfo.DeclaringType!);
             if (metadataType != null)
             {
-                MemberInfo metadataTypeMemberInfo = ReflectionUtils.GetMemberInfoFromType(metadataType, memberInfo);
+                MemberInfo? metadataTypeMemberInfo = ReflectionUtils.GetMemberInfoFromType(metadataType, memberInfo);
 
                 if (metadataTypeMemberInfo != null)
                 {
@@ -373,7 +374,7 @@ namespace Newtonsoft.Json.Serialization
             {
                 foreach (Type typeInterface in memberInfo.DeclaringType.GetInterfaces())
                 {
-                    MemberInfo interfaceTypeMemberInfo = ReflectionUtils.GetMemberInfoFromType(typeInterface, memberInfo);
+                    MemberInfo? interfaceTypeMemberInfo = ReflectionUtils.GetMemberInfoFromType(typeInterface, memberInfo);
 
                     if (interfaceTypeMemberInfo != null)
                     {
@@ -459,7 +460,9 @@ namespace Newtonsoft.Json.Serialization
             {
                 if (_dynamicCodeGeneration == null)
                 {
-#if HAVE_CAS
+#if HAVE_DYNAMIC_CODE_COMPILED
+                    _dynamicCodeGeneration = RuntimeFeature.IsDynamicCodeCompiled;
+#elif HAVE_CAS
                     try
                     {
                         new ReflectionPermission(ReflectionPermissionFlag.MemberAccess).Demand();

Src/Newtonsoft.Json/Serialization/NamingStrategy.cs

@@ -123,7 +123,7 @@ namespace Newtonsoft.Json.Serialization
         /// </summary>
         /// <param name="obj"></param>
         /// <returns></returns>
-        public override bool Equals(object obj) => Equals(obj as NamingStrategy);
+        public override bool Equals(object? obj) => Equals(obj as NamingStrategy);
 
         /// <summary>
         /// Compare to another NamingStrategy

Src/Newtonsoft.Json/Serialization/SerializationBinderAdapter.cs

@@ -43,7 +43,7 @@ namespace Newtonsoft.Json.Serialization
 
         public Type BindToType(string? assemblyName, string typeName)
         {
-            return SerializationBinder.BindToType(assemblyName, typeName);
+            return SerializationBinder.BindToType(assemblyName!, typeName)!;
         }
 
         public void BindToName(Type serializedType, out string? assemblyName, out string? typeName)

Src/Newtonsoft.Json/Utilities/AsyncUtils.cs

@@ -95,11 +95,11 @@ namespace Newtonsoft.Json.Utilities
             return cancellationToken.IsCancellationRequested ? FromCanceled<int>(cancellationToken) : reader.ReadAsync(buffer, index, count);
         }
 
-        public static bool IsCompletedSucessfully(this Task task)
+        public static bool IsCompletedSuccessfully(this Task task)
         {
             // IsCompletedSucessfully is the faster method, but only currently exposed on .NET Core 2.0
-#if NETCOREAPP2_0
-            return task.IsCompletedSucessfully;
+#if NETCOREAPP2_0_OR_GREATER
+            return task.IsCompletedSuccessfully;
 #else
             return task.Status == TaskStatus.RanToCompletion;
 #endif

Src/Newtonsoft.Json/Utilities/Base64Encoder.cs

@@ -78,12 +78,12 @@ namespace Newtonsoft.Json.Utilities
 
             if (_leftOverBytesCount > 0)
             {
-                if(FulfillFromLeftover(buffer, index, ref count))
+                if (FulfillFromLeftover(buffer, index, ref count))
                 {
                     return;
                 }
 
-                int num2 = Convert.ToBase64CharArray(_leftOverBytes, 0, 3, _charsLine, 0);
+                int num2 = Convert.ToBase64CharArray(_leftOverBytes!, 0, 3, _charsLine, 0);
                 WriteChars(_charsLine, 0, num2);
             }
 
@@ -145,7 +145,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_leftOverBytesCount > 0)
             {
-                int count = Convert.ToBase64CharArray(_leftOverBytes, 0, _leftOverBytesCount, _charsLine, 0);
+                int count = Convert.ToBase64CharArray(_leftOverBytes!, 0, _leftOverBytesCount, _charsLine, 0);
                 WriteChars(_charsLine, 0, count);
                 _leftOverBytesCount = 0;
             }
@@ -169,7 +169,7 @@ namespace Newtonsoft.Json.Utilities
                     return;
                 }
 
-                int num2 = Convert.ToBase64CharArray(_leftOverBytes, 0, 3, _charsLine, 0);
+                int num2 = Convert.ToBase64CharArray(_leftOverBytes!, 0, 3, _charsLine, 0);
                 await WriteCharsAsync(_charsLine, 0, num2, cancellationToken).ConfigureAwait(false);
             }
 
@@ -203,7 +203,7 @@ namespace Newtonsoft.Json.Utilities
 
             if (_leftOverBytesCount > 0)
             {
-                int count = Convert.ToBase64CharArray(_leftOverBytes, 0, _leftOverBytesCount, _charsLine, 0);
+                int count = Convert.ToBase64CharArray(_leftOverBytes!, 0, _leftOverBytesCount, _charsLine, 0);
                 _leftOverBytesCount = 0;
                 return WriteCharsAsync(_charsLine, 0, count, cancellationToken);
             }

Src/Newtonsoft.Json/Utilities/BidirectionalDictionary.cs

@@ -25,11 +25,14 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 
 namespace Newtonsoft.Json.Utilities
 {
     internal class BidirectionalDictionary<TFirst, TSecond>
+        where TFirst : notnull
+        where TSecond : notnull
     {
         private readonly IDictionary<TFirst, TSecond> _firstToSecond;
         private readonly IDictionary<TSecond, TFirst> _secondToFirst;
@@ -61,7 +64,7 @@ namespace Newtonsoft.Json.Utilities
 
         public void Set(TFirst first, TSecond second)
         {
-            if (_firstToSecond.TryGetValue(first, out TSecond existingSecond))
+            if (_firstToSecond.TryGetValue(first, out TSecond? existingSecond))
             {
                 if (!existingSecond!.Equals(second))
                 {
@@ -69,7 +72,7 @@ namespace Newtonsoft.Json.Utilities
                 }
             }
 
-            if (_secondToFirst.TryGetValue(second, out TFirst existingFirst))
+            if (_secondToFirst.TryGetValue(second, out TFirst? existingFirst))
             {
                 if (!existingFirst!.Equals(first))
                 {
@@ -81,12 +84,12 @@ namespace Newtonsoft.Json.Utilities
             _secondToFirst.Add(second, first);
         }
 
-        public bool TryGetByFirst(TFirst first, out TSecond second)
+        public bool TryGetByFirst(TFirst first, [NotNullWhen(true)] out TSecond? second)
         {
             return _firstToSecond.TryGetValue(first, out second);
         }
 
-        public bool TryGetBySecond(TSecond second, out TFirst first)
+        public bool TryGetBySecond(TSecond second, [NotNullWhen(true)] out TFirst? first)
         {
             return _secondToFirst.TryGetValue(second, out first);
         }

Src/Newtonsoft.Json/Utilities/CollectionUtils.cs

@@ -289,7 +289,7 @@ namespace Newtonsoft.Json.Utilities
                     break;
                 }
 
-                object v = currentArray[0];
+                object? v = currentArray[0];
                 if (v is IList list)
                 {
                     currentArray = list;
@@ -341,11 +341,11 @@ namespace Newtonsoft.Json.Utilities
                 int index = indices[i];
                 if (i == indices.Length - 1)
                 {
-                    return currentList[index];
+                    return currentList[index]!;
                 }
                 else
                 {
-                    currentList = (IList)currentList[index];
+                    currentList = (IList)currentList[index]!;
                 }
             }
             return currentList;
@@ -368,15 +368,21 @@ namespace Newtonsoft.Json.Utilities
 
         public static T[] ArrayEmpty<T>()
         {
+#if !HAS_ARRAY_EMPTY
             // Enumerable.Empty<T> no longer returns an empty array in .NET Core 3.0
             return EmptyArrayContainer<T>.Empty;
+#else
+            return Array.Empty<T>();
+#endif
         }
 
+#if !HAS_ARRAY_EMPTY
         private static class EmptyArrayContainer<T>
         {
 #pragma warning disable CA1825 // Avoid zero-length array allocations.
             public static readonly T[] Empty = new T[0];
 #pragma warning restore CA1825 // Avoid zero-length array allocations.
         }
+#endif
     }
 }

Src/Newtonsoft.Json/Utilities/CollectionWrapper.cs

@@ -168,7 +168,7 @@ namespace Newtonsoft.Json.Utilities
 
         public virtual IEnumerator<T> GetEnumerator()
         {
-            return (_genericCollection ?? _list.Cast<T>()).GetEnumerator();
+            return (_genericCollection ?? _list!.Cast<T>()).GetEnumerator();
         }
 
         IEnumerator IEnumerable.GetEnumerator()
@@ -176,25 +176,25 @@ namespace Newtonsoft.Json.Utilities
             return ((IEnumerable)_genericCollection! ?? _list!).GetEnumerator();
         }
 
-        int IList.Add(object value)
+        int IList.Add(object? value)
         {
             VerifyValueType(value);
-            Add((T)value);
+            Add((T)value!);
 
             return (Count - 1);
         }
 
-        bool IList.Contains(object value)
+        bool IList.Contains(object? value)
         {
             if (IsCompatibleObject(value))
             {
-                return Contains((T)value);
+                return Contains((T)value!);
             }
 
             return false;
         }
 
-        int IList.IndexOf(object value)
+        int IList.IndexOf(object? value)
         {
             if (_genericCollection != null)
             {
@@ -203,7 +203,7 @@ namespace Newtonsoft.Json.Utilities
 
             if (IsCompatibleObject(value))
             {
-                return _list!.IndexOf((T)value);
+                return _list!.IndexOf((T)value!);
             }
 
             return -1;
@@ -219,7 +219,7 @@ namespace Newtonsoft.Json.Utilities
             _list!.RemoveAt(index);
         }
 
-        void IList.Insert(int index, object value)
+        void IList.Insert(int index, object? value)
         {
             if (_genericCollection != null)
             {
@@ -227,7 +227,7 @@ namespace Newtonsoft.Json.Utilities
             }
 
             VerifyValueType(value);
-            _list!.Insert(index, (T)value);
+            _list!.Insert(index, (T)value!);
         }
 
         bool IList.IsFixedSize
@@ -246,15 +246,15 @@ namespace Newtonsoft.Json.Utilities
             }
         }
 
-        void IList.Remove(object value)
+        void IList.Remove(object? value)
         {
             if (IsCompatibleObject(value))
             {
-                Remove((T)value);
+                Remove((T)value!);
             }
         }
 
-        object IList.this[int index]
+        object? IList.this[int index]
         {
             get
             {
@@ -273,7 +273,7 @@ namespace Newtonsoft.Json.Utilities
                 }
 
                 VerifyValueType(value);
-                _list![index] = (T)value;
+                _list![index] = (T?)value;
             }
         }
 
@@ -297,7 +297,7 @@ namespace Newtonsoft.Json.Utilities
             }
         }
 
-        private static void VerifyValueType(object value)
+        private static void VerifyValueType(object? value)
         {
             if (!IsCompatibleObject(value))
             {
@@ -305,7 +305,7 @@ namespace Newtonsoft.Json.Utilities
             }
         }
 
-        private static bool IsCompatibleObject(object value)
+        private static bool IsCompatibleObject(object? value)
         {
             if (!(value is T) && (value != null || (typeof(T).IsValueType() && !ReflectionUtils.IsNullableType(typeof(T)))))
             {

Src/Newtonsoft.Json/Utilities/ConvertUtils.cs

@@ -215,7 +215,7 @@ namespace Newtonsoft.Json.Utilities
             // performance?
             if (ReflectionUtils.IsNullableType(t))
             {
-                Type nonNullable = Nullable.GetUnderlyingType(t);
+                Type nonNullable = Nullable.GetUnderlyingType(t)!;
                 if (nonNullable.IsEnum())
                 {
                     Type nullableUnderlyingType = typeof(Nullable<>).MakeGenericType(Enum.GetUnderlyingType(nonNullable));
@@ -263,7 +263,7 @@ namespace Newtonsoft.Json.Utilities
         {
             Type initialType = t.Value1;
             Type targetType = t.Value2;
-            MethodInfo castMethodInfo = targetType.GetMethod("op_Implicit", new[] { initialType })
+            MethodInfo? castMethodInfo = targetType.GetMethod("op_Implicit", new[] { initialType })
                 ?? targetType.GetMethod("op_Explicit", new[] { initialType });
 
             if (castMethodInfo == null)
@@ -414,7 +414,7 @@ namespace Newtonsoft.Json.Utilities
 
             if (ReflectionUtils.IsNullableType(targetType))
             {
-                targetType = Nullable.GetUnderlyingType(targetType);
+                targetType = Nullable.GetUnderlyingType(targetType)!;
             }
 
             Type initialType = initialValue.GetType();
@@ -432,7 +432,7 @@ namespace Newtonsoft.Json.Utilities
                 {
                     if (initialValue is string)
                     {
-                        value = Enum.Parse(targetType, initialValue.ToString(), true);
+                        value = Enum.Parse(targetType, initialValue.ToString()!, true);
                         return ConvertResult.Success;
                     }
                     else if (IsInteger(initialValue))

Src/Newtonsoft.Json/Utilities/DictionaryWrapper.cs

@@ -89,7 +89,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                _dictionary.Add(key, value);
+                _dictionary.Add(key!, value);
             }
             else if (_genericDictionary != null)
             {
@@ -105,7 +105,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                return _dictionary.Contains(key);
+                return _dictionary.Contains(key!);
             }
 #if HAVE_READ_ONLY_COLLECTIONS
             else if (_readOnlyDictionary != null)
@@ -144,9 +144,9 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                if (_dictionary.Contains(key))
+                if (_dictionary.Contains(key!))
                 {
-                    _dictionary.Remove(key);
+                    _dictionary.Remove(key!);
                     return true;
                 }
                 else
@@ -172,7 +172,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                if (!_dictionary.Contains(key))
+                if (!_dictionary.Contains(key!))
                 {
 #pragma warning disable CS8653 // A default expression introduces a null value for a type parameter.
                     value = default;
@@ -181,7 +181,7 @@ namespace Newtonsoft.Json.Utilities
                 }
                 else
                 {
-                    value = (TValue)_dictionary[key];
+                    value = (TValue)_dictionary[key!]!;
                     return true;
                 }
             }
@@ -224,7 +224,7 @@ namespace Newtonsoft.Json.Utilities
             {
                 if (_dictionary != null)
                 {
-                    return (TValue)_dictionary[key];
+                    return (TValue)_dictionary[key!]!;
                 }
 #if HAVE_READ_ONLY_COLLECTIONS
                 else if (_readOnlyDictionary != null)
@@ -241,7 +241,7 @@ namespace Newtonsoft.Json.Utilities
             {
                 if (_dictionary != null)
                 {
-                    _dictionary[key] = value;
+                    _dictionary[key!] = value;
                 }
 #if HAVE_READ_ONLY_COLLECTIONS
                 else if (_readOnlyDictionary != null)
@@ -321,7 +321,7 @@ namespace Newtonsoft.Json.Utilities
                     while (e.MoveNext())
                     {
                         DictionaryEntry entry = e.Entry;
-                        array[arrayIndex++] = new KeyValuePair<TKey, TValue>((TKey)entry.Key, (TValue)entry.Value);
+                        array[arrayIndex++] = new KeyValuePair<TKey, TValue>((TKey)entry.Key, (TValue)entry.Value!);
                     }
                 }
                 finally
@@ -387,13 +387,13 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                if (_dictionary.Contains(item.Key))
+                if (_dictionary.Contains(item.Key!))
                 {
-                    object value = _dictionary[item.Key];
+                    object? value = _dictionary[item.Key!];
 
                     if (Equals(value, item.Value))
                     {
-                        _dictionary.Remove(item.Key);
+                        _dictionary.Remove(item.Key!);
                         return true;
                     }
                     else
@@ -422,7 +422,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (_dictionary != null)
             {
-                return _dictionary.Cast<DictionaryEntry>().Select(de => new KeyValuePair<TKey, TValue>((TKey)de.Key, (TValue)de.Value)).GetEnumerator();
+                return _dictionary.Cast<DictionaryEntry>().Select(de => new KeyValuePair<TKey, TValue>((TKey)de.Key, (TValue)de.Value!)).GetEnumerator();
             }
 #if HAVE_READ_ONLY_COLLECTIONS
             else if (_readOnlyDictionary != null)
@@ -441,7 +441,7 @@ namespace Newtonsoft.Json.Utilities
             return GetEnumerator();
         }
 
-        void IDictionary.Add(object key, object value)
+        void IDictionary.Add(object key, object? value)
         {
             if (_dictionary != null)
             {
@@ -455,7 +455,7 @@ namespace Newtonsoft.Json.Utilities
 #endif
             else
             {
-                GenericDictionary.Add((TKey)key, (TValue)value);
+                GenericDictionary.Add((TKey)key, (TValue)value!);
             }
         }
 
@@ -517,9 +517,9 @@ namespace Newtonsoft.Json.Utilities
 
             public object Key => Entry.Key;
 
-            public object Value => Entry.Value;
+            public object? Value => Entry.Value;
 
-            public object Current => new DictionaryEntry(_e.Current.Key, _e.Current.Value);
+            public object Current => new DictionaryEntry(_e.Current.Key!, _e.Current.Value);
 
             public bool MoveNext()
             {

Src/Newtonsoft.Json/Utilities/DynamicProxyMetaObject.cs

@@ -37,7 +37,7 @@ namespace Newtonsoft.Json.Utilities
         private readonly DynamicProxy<T> _proxy;
 
         internal DynamicProxyMetaObject(Expression expression, T value, DynamicProxy<T> proxy)
-            : base(expression, BindingRestrictions.Empty, value)
+            : base(expression, BindingRestrictions.Empty, value!)
         {
             _proxy = proxy;
         }
@@ -109,7 +109,7 @@ namespace Newtonsoft.Json.Utilities
                     new GetBinderAdapter(binder),
                     NoArgs,
                     fallback(null),
-                    e => binder.FallbackInvoke(e, args, null)
+                    e => binder.FallbackInvoke(e!, args, null)
                     ),
                 null
                 );
@@ -197,7 +197,7 @@ namespace Newtonsoft.Json.Utilities
             Type t = binder.GetType();
             while (!t.IsVisible())
             {
-                t = t.BaseType();
+                t = t.BaseType()!;
             }
             return Expression.Constant(binder, t);
         }
@@ -256,7 +256,7 @@ namespace Newtonsoft.Json.Utilities
                     Expression.Condition(
                         Expression.Call(
                             Expression.Constant(_proxy),
-                            typeof(DynamicProxy<T>).GetMethod(methodName),
+                            typeof(DynamicProxy<T>).GetMethod(methodName)!,
                             callArgs
                             ),
                         resultMetaObject.Expression,
@@ -304,7 +304,7 @@ namespace Newtonsoft.Json.Utilities
                     Expression.Condition(
                         Expression.Call(
                             Expression.Constant(_proxy),
-                            typeof(DynamicProxy<T>).GetMethod(methodName),
+                            typeof(DynamicProxy<T>).GetMethod(methodName)!,
                             callArgs
                             ),
                         result,
@@ -342,7 +342,7 @@ namespace Newtonsoft.Json.Utilities
                 Expression.Condition(
                     Expression.Call(
                         Expression.Constant(_proxy),
-                        typeof(DynamicProxy<T>).GetMethod(methodName),
+                        typeof(DynamicProxy<T>).GetMethod(methodName)!,
                         callArgs
                         ),
                     Expression.Empty(),
@@ -366,7 +366,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override IEnumerable<string> GetDynamicMemberNames()
         {
-            return _proxy.GetDynamicMemberNames((T)Value);
+            return _proxy.GetDynamicMemberNames((T)Value!);
         }
 
         // It is okay to throw NotSupported from this binder. This object
@@ -380,7 +380,7 @@ namespace Newtonsoft.Json.Utilities
             {
             }
 
-            public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
+            public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject? errorSuggestion)
             {
                 throw new NotSupportedException();
             }

Src/Newtonsoft.Json/Utilities/DynamicReflectionDelegateFactory.cs

@@ -51,7 +51,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override ObjectConstructor<object> CreateParameterizedConstructor(MethodBase method)
         {
-            DynamicMethod dynamicMethod = CreateDynamicMethod(method.ToString(), typeof(object), new[] { typeof(object[]) }, method.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod(method.ToString()!, typeof(object), new[] { typeof(object[]) }, method.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateMethodCallIL(method, generator, 0);
@@ -61,7 +61,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override MethodCall<T, object?> CreateMethodCall<T>(MethodBase method)
         {
-            DynamicMethod dynamicMethod = CreateDynamicMethod(method.ToString(), typeof(object), new[] { typeof(object), typeof(object[]) }, method.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod(method.ToString()!, typeof(object), new[] { typeof(object), typeof(object[]) }, method.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateMethodCallIL(method, generator, 1);
@@ -80,14 +80,14 @@ namespace Newtonsoft.Json.Utilities
             generator.Emit(OpCodes.Ldlen);
             generator.Emit(OpCodes.Ldc_I4, args.Length);
             generator.Emit(OpCodes.Beq, argsOk);
-            generator.Emit(OpCodes.Newobj, typeof(TargetParameterCountException).GetConstructor(ReflectionUtils.EmptyTypes));
+            generator.Emit(OpCodes.Newobj, typeof(TargetParameterCountException).GetConstructor(ReflectionUtils.EmptyTypes)!);
             generator.Emit(OpCodes.Throw);
 
             generator.MarkLabel(argsOk);
 
             if (!method.IsConstructor && !method.IsStatic)
             {
-                generator.PushInstance(method.DeclaringType);
+                generator.PushInstance(method.DeclaringType!);
             }
 
             LocalBuilder localConvertible = generator.DeclareLocal(typeof(IConvertible));
@@ -103,7 +103,7 @@ namespace Newtonsoft.Json.Utilities
 
                 if (parameterType.IsByRef)
                 {
-                    parameterType = parameterType.GetElementType();
+                    parameterType = parameterType.GetElementType()!;
 
                     LocalBuilder localVariable = generator.DeclareLocal(parameterType);
 
@@ -170,7 +170,7 @@ namespace Newtonsoft.Json.Utilities
                     if (parameterType.IsPrimitive())
                     {
                         // for primitive types we need to handle type widening (e.g. short -> int)
-                        MethodInfo toParameterTypeMethod = typeof(IConvertible)
+                        MethodInfo? toParameterTypeMethod = typeof(IConvertible)
                             .GetMethod("To" + parameterType.Name, new[] { typeof(IFormatProvider) });
                         
                         if (toParameterTypeMethod != null)
@@ -227,7 +227,7 @@ namespace Newtonsoft.Json.Utilities
             }
 
             Type returnType = method.IsConstructor
-                ? method.DeclaringType
+                ? method.DeclaringType!
                 : ((MethodInfo)method).ReturnType;
 
             if (returnType != typeof(void))
@@ -268,7 +268,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                ConstructorInfo constructorInfo =
+                ConstructorInfo? constructorInfo =
                     type.GetConstructor(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, ReflectionUtils.EmptyTypes, null);
 
                 if (constructorInfo == null)
@@ -284,7 +284,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override Func<T, object?> CreateGet<T>(PropertyInfo propertyInfo)
         {
-            DynamicMethod dynamicMethod = CreateDynamicMethod("Get" + propertyInfo.Name, typeof(object), new[] { typeof(T) }, propertyInfo.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod("Get" + propertyInfo.Name, typeof(object), new[] { typeof(T) }, propertyInfo.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateGetPropertyIL(propertyInfo, generator);
@@ -294,7 +294,7 @@ namespace Newtonsoft.Json.Utilities
 
         private void GenerateCreateGetPropertyIL(PropertyInfo propertyInfo, ILGenerator generator)
         {
-            MethodInfo getMethod = propertyInfo.GetGetMethod(true);
+            MethodInfo? getMethod = propertyInfo.GetGetMethod(true);
             if (getMethod == null)
             {
                 throw new ArgumentException("Property '{0}' does not have a getter.".FormatWith(CultureInfo.InvariantCulture, propertyInfo.Name));
@@ -302,7 +302,7 @@ namespace Newtonsoft.Json.Utilities
 
             if (!getMethod.IsStatic)
             {
-                generator.PushInstance(propertyInfo.DeclaringType);
+                generator.PushInstance(propertyInfo.DeclaringType!);
             }
 
             generator.CallMethod(getMethod);
@@ -314,12 +314,12 @@ namespace Newtonsoft.Json.Utilities
         {
             if (fieldInfo.IsLiteral)
             {
-                object constantValue = fieldInfo.GetValue(null);
+                object constantValue = fieldInfo.GetValue(null)!;
                 Func<T, object?> getter = o => constantValue;
                 return getter;
             }
 
-            DynamicMethod dynamicMethod = CreateDynamicMethod("Get" + fieldInfo.Name, typeof(T), new[] { typeof(object) }, fieldInfo.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod("Get" + fieldInfo.Name, typeof(T), new[] { typeof(object) }, fieldInfo.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateGetFieldIL(fieldInfo, generator);
@@ -331,7 +331,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (!fieldInfo.IsStatic)
             {
-                generator.PushInstance(fieldInfo.DeclaringType);
+                generator.PushInstance(fieldInfo.DeclaringType!);
                 generator.Emit(OpCodes.Ldfld, fieldInfo);
             }
             else
@@ -345,7 +345,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override Action<T, object?> CreateSet<T>(FieldInfo fieldInfo)
         {
-            DynamicMethod dynamicMethod = CreateDynamicMethod("Set" + fieldInfo.Name, null, new[] { typeof(T), typeof(object) }, fieldInfo.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod("Set" + fieldInfo.Name, null, new[] { typeof(T), typeof(object) }, fieldInfo.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateSetFieldIL(fieldInfo, generator);
@@ -357,7 +357,7 @@ namespace Newtonsoft.Json.Utilities
         {
             if (!fieldInfo.IsStatic)
             {
-                generator.PushInstance(fieldInfo.DeclaringType);
+                generator.PushInstance(fieldInfo.DeclaringType!);
             }
 
             generator.Emit(OpCodes.Ldarg_1);
@@ -377,7 +377,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override Action<T, object?> CreateSet<T>(PropertyInfo propertyInfo)
         {
-            DynamicMethod dynamicMethod = CreateDynamicMethod("Set" + propertyInfo.Name, null, new[] { typeof(T), typeof(object) }, propertyInfo.DeclaringType);
+            DynamicMethod dynamicMethod = CreateDynamicMethod("Set" + propertyInfo.Name, null, new[] { typeof(T), typeof(object) }, propertyInfo.DeclaringType!);
             ILGenerator generator = dynamicMethod.GetILGenerator();
 
             GenerateCreateSetPropertyIL(propertyInfo, generator);
@@ -387,10 +387,10 @@ namespace Newtonsoft.Json.Utilities
 
         internal static void GenerateCreateSetPropertyIL(PropertyInfo propertyInfo, ILGenerator generator)
         {
-            MethodInfo setMethod = propertyInfo.GetSetMethod(true);
+            MethodInfo setMethod = propertyInfo.GetSetMethod(true)!;
             if (!setMethod.IsStatic)
             {
-                generator.PushInstance(propertyInfo.DeclaringType);
+                generator.PushInstance(propertyInfo.DeclaringType!);
             }
 
             generator.Emit(OpCodes.Ldarg_1);

Src/Newtonsoft.Json/Utilities/DynamicUtils.cs

@@ -64,7 +64,7 @@ namespace Newtonsoft.Json.Utilities
             {
                 if (!_init)
                 {
-                    Type binderType = Type.GetType(BinderTypeName, false);
+                    Type? binderType = Type.GetType(BinderTypeName, false);
                     if (binderType == null)
                     {
                         throw new InvalidOperationException("Could not resolve type '{0}'. You may need to add a reference to Microsoft.CSharp.dll to work with dynamic types.".FormatWith(CultureInfo.InvariantCulture, BinderTypeName));
@@ -82,15 +82,15 @@ namespace Newtonsoft.Json.Utilities
 
             private static object CreateSharpArgumentInfoArray(params int[] values)
             {
-                Type csharpArgumentInfoType = Type.GetType(CSharpArgumentInfoTypeName);
-                Type csharpArgumentInfoFlags = Type.GetType(CSharpArgumentInfoFlagsTypeName);
+                Type csharpArgumentInfoType = Type.GetType(CSharpArgumentInfoTypeName, true)!;
+                Type csharpArgumentInfoFlags = Type.GetType(CSharpArgumentInfoFlagsTypeName, true)!;
 
                 Array a = Array.CreateInstance(csharpArgumentInfoType, values.Length);
 
                 for (int i = 0; i < values.Length; i++)
                 {
-                    MethodInfo createArgumentInfoMethod = csharpArgumentInfoType.GetMethod("Create", new[] { csharpArgumentInfoFlags, typeof(string) });
-                    object arg = createArgumentInfoMethod.Invoke(null, new object?[] { 0, null });
+                    MethodInfo createArgumentInfoMethod = csharpArgumentInfoType.GetMethod("Create", new[] { csharpArgumentInfoFlags, typeof(string) })!;
+                    object arg = createArgumentInfoMethod.Invoke(null, new object?[] { 0, null })!;
                     a.SetValue(arg, i);
                 }
 
@@ -99,16 +99,16 @@ namespace Newtonsoft.Json.Utilities
 
             private static void CreateMemberCalls()
             {
-                Type csharpArgumentInfoType = Type.GetType(CSharpArgumentInfoTypeName, true);
-                Type csharpBinderFlagsType = Type.GetType(CSharpBinderFlagsTypeName, true);
-                Type binderType = Type.GetType(BinderTypeName, true);
+                Type csharpArgumentInfoType = Type.GetType(CSharpArgumentInfoTypeName, true)!;
+                Type csharpBinderFlagsType = Type.GetType(CSharpBinderFlagsTypeName, true)!;
+                Type binderType = Type.GetType(BinderTypeName, true)!;
 
                 Type csharpArgumentInfoTypeEnumerableType = typeof(IEnumerable<>).MakeGenericType(csharpArgumentInfoType);
 
-                MethodInfo getMemberMethod = binderType.GetMethod("GetMember", new[] { csharpBinderFlagsType, typeof(string), typeof(Type), csharpArgumentInfoTypeEnumerableType });
+                MethodInfo getMemberMethod = binderType.GetMethod("GetMember", new[] { csharpBinderFlagsType, typeof(string), typeof(Type), csharpArgumentInfoTypeEnumerableType })!;
                 _getMemberCall = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(getMemberMethod);
 
-                MethodInfo setMemberMethod = binderType.GetMethod("SetMember", new[] { csharpBinderFlagsType, typeof(string), typeof(Type), csharpArgumentInfoTypeEnumerableType });
+                MethodInfo setMemberMethod = binderType.GetMethod("SetMember", new[] { csharpBinderFlagsType, typeof(string), typeof(Type), csharpArgumentInfoTypeEnumerableType })!;
                 _setMemberCall = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(setMemberMethod);
             }
 #endif
@@ -161,7 +161,7 @@ namespace Newtonsoft.Json.Utilities
             _innerBinder = innerBinder;
         }
 
-        public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
+        public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject? errorSuggestion)
         {
             DynamicMetaObject retMetaObject = _innerBinder.Bind(target, CollectionUtils.ArrayEmpty<DynamicMetaObject>());
 
@@ -183,7 +183,7 @@ namespace Newtonsoft.Json.Utilities
             _innerBinder = innerBinder;
         }
 
-        public override DynamicMetaObject FallbackSetMember(DynamicMetaObject target, DynamicMetaObject value, DynamicMetaObject errorSuggestion)
+        public override DynamicMetaObject FallbackSetMember(DynamicMetaObject target, DynamicMetaObject value, DynamicMetaObject? errorSuggestion)
         {
             DynamicMetaObject retMetaObject = _innerBinder.Bind(target, new DynamicMetaObject[] { value });
 

Src/Newtonsoft.Json/Utilities/EnumUtils.cs

@@ -60,11 +60,11 @@ namespace Newtonsoft.Json.Utilities
             {
                 string name = names[i];
                 FieldInfo f = enumType.GetField(name, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static)!;
-                values[i] = ToUInt64(f.GetValue(null));
+                values[i] = ToUInt64(f.GetValue(null)!);
 
                 string resolvedName;
 #if HAVE_DATA_CONTRACTS
-                string specifiedName = f.GetCustomAttributes(typeof(EnumMemberAttribute), true)
+                string? specifiedName = f.GetCustomAttributes(typeof(EnumMemberAttribute), true)
                          .Cast<EnumMemberAttribute>()
                          .Select(a => a.Value)
                          .SingleOrDefault();

Src/Newtonsoft.Json/Utilities/ExpressionReflectionDelegateFactory.cs

@@ -111,7 +111,7 @@ namespace Newtonsoft.Json.Utilities
                     bool isByRef = false;
                     if (parameterType.IsByRef)
                     {
-                        parameterType = parameterType.GetElementType();
+                        parameterType = parameterType.GetElementType()!;
                         isByRef = true;
                     }
 
@@ -144,7 +144,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                Expression readParameter = EnsureCastExpression(targetParameterExpression!, method.DeclaringType);
+                Expression readParameter = EnsureCastExpression(targetParameterExpression!, method.DeclaringType!);
 
                 callExpression = Expression.Call(readParameter, (MethodInfo)method, argsExpression);
             }
@@ -194,7 +194,7 @@ namespace Newtonsoft.Json.Utilities
             // avoid error from expressions compiler because of abstract class
             if (type.IsAbstract())
             {
-                return () => (T)Activator.CreateInstance(type);
+                return () => (T)Activator.CreateInstance(type)!;
             }
 
             try
@@ -214,7 +214,7 @@ namespace Newtonsoft.Json.Utilities
             {
                 // an error can be thrown if constructor is not valid on Win8
                 // will have INVOCATION_FLAGS_NON_W8P_FX_API invocation flag
-                return () => (T)Activator.CreateInstance(type);
+                return () => (T)Activator.CreateInstance(type)!;
             }
         }
 
@@ -240,7 +240,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                Expression readParameter = EnsureCastExpression(parameterExpression, propertyInfo.DeclaringType);
+                Expression readParameter = EnsureCastExpression(parameterExpression, propertyInfo.DeclaringType!);
 
                 resultExpression = Expression.MakeMemberAccess(readParameter, propertyInfo);
             }
@@ -266,7 +266,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                Expression sourceExpression = EnsureCastExpression(sourceParameter, fieldInfo.DeclaringType);
+                Expression sourceExpression = EnsureCastExpression(sourceParameter, fieldInfo.DeclaringType!);
 
                 fieldExpression = Expression.Field(sourceExpression, fieldInfo);
             }
@@ -283,7 +283,7 @@ namespace Newtonsoft.Json.Utilities
 
             // use reflection for structs
             // expression doesn't correctly set value
-            if (fieldInfo.DeclaringType.IsValueType() || fieldInfo.IsInitOnly)
+            if (fieldInfo.DeclaringType!.IsValueType() || fieldInfo.IsInitOnly)
             {
                 return LateBoundReflectionDelegateFactory.Instance.CreateSet<T>(fieldInfo);
             }
@@ -298,7 +298,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                Expression sourceExpression = EnsureCastExpression(sourceParameterExpression, fieldInfo.DeclaringType);
+                Expression sourceExpression = EnsureCastExpression(sourceParameterExpression, fieldInfo.DeclaringType!);
 
                 fieldExpression = Expression.Field(sourceExpression, fieldInfo);
             }
@@ -319,7 +319,7 @@ namespace Newtonsoft.Json.Utilities
 
             // use reflection for structs
             // expression doesn't correctly set value
-            if (propertyInfo.DeclaringType.IsValueType())
+            if (propertyInfo.DeclaringType!.IsValueType())
             {
                 return LateBoundReflectionDelegateFactory.Instance.CreateSet<T>(propertyInfo);
             }
@@ -345,7 +345,7 @@ namespace Newtonsoft.Json.Utilities
             }
             else
             {
-                Expression readInstanceParameter = EnsureCastExpression(instanceParameter, propertyInfo.DeclaringType);
+                Expression readInstanceParameter = EnsureCastExpression(instanceParameter, propertyInfo.DeclaringType!);
 
                 setExpression = Expression.Call(readInstanceParameter, setMethod, readValueParameter);
             }
@@ -372,7 +372,7 @@ namespace Newtonsoft.Json.Utilities
 
                 if (allowWidening && targetType.IsPrimitive())
                 {
-                    MethodInfo toTargetTypeMethod = typeof(Convert)
+                    MethodInfo? toTargetTypeMethod = typeof(Convert)
                         .GetMethod("To" + targetType.Name, new[] { typeof(object) });
 
                     if (toTargetTypeMethod != null)

Src/Newtonsoft.Json/Utilities/FSharpUtils.cs

@@ -60,7 +60,7 @@ namespace Newtonsoft.Json.Utilities
         {
             FSharpCoreAssembly = fsharpCoreAssembly;
 
-            Type fsharpType = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.FSharpType");
+            Type fsharpType = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.FSharpType")!;
 
             MethodInfo isUnionMethodInfo = GetMethodWithNonPublicFallback(fsharpType, "IsUnion", BindingFlags.Public | BindingFlags.Static);
             IsUnion = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(isUnionMethodInfo)!;
@@ -68,23 +68,23 @@ namespace Newtonsoft.Json.Utilities
             MethodInfo getUnionCasesMethodInfo = GetMethodWithNonPublicFallback(fsharpType, "GetUnionCases", BindingFlags.Public | BindingFlags.Static);
             GetUnionCases = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(getUnionCasesMethodInfo)!;
 
-            Type fsharpValue = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.FSharpValue");
+            Type fsharpValue = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.FSharpValue")!;
 
             PreComputeUnionTagReader = CreateFSharpFuncCall(fsharpValue, "PreComputeUnionTagReader");
             PreComputeUnionReader = CreateFSharpFuncCall(fsharpValue, "PreComputeUnionReader");
             PreComputeUnionConstructor = CreateFSharpFuncCall(fsharpValue, "PreComputeUnionConstructor");
 
-            Type unionCaseInfo = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.UnionCaseInfo");
+            Type unionCaseInfo = fsharpCoreAssembly.GetType("Microsoft.FSharp.Reflection.UnionCaseInfo")!;
 
             GetUnionCaseInfoName = JsonTypeReflector.ReflectionDelegateFactory.CreateGet<object>(unionCaseInfo.GetProperty("Name")!)!;
             GetUnionCaseInfoTag = JsonTypeReflector.ReflectionDelegateFactory.CreateGet<object>(unionCaseInfo.GetProperty("Tag")!)!;
             GetUnionCaseInfoDeclaringType = JsonTypeReflector.ReflectionDelegateFactory.CreateGet<object>(unionCaseInfo.GetProperty("DeclaringType")!)!;
-            GetUnionCaseInfoFields = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object>(unionCaseInfo.GetMethod("GetFields"));
+            GetUnionCaseInfoFields = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object>(unionCaseInfo.GetMethod("GetFields")!);
 
-            Type listModule = fsharpCoreAssembly.GetType("Microsoft.FSharp.Collections.ListModule");
-            _ofSeq = listModule.GetMethod("OfSeq");
+            Type listModule = fsharpCoreAssembly.GetType("Microsoft.FSharp.Collections.ListModule")!;
+            _ofSeq = listModule.GetMethod("OfSeq")!;
 
-            _mapType = fsharpCoreAssembly.GetType("Microsoft.FSharp.Collections.FSharpMap`2");
+            _mapType = fsharpCoreAssembly.GetType("Microsoft.FSharp.Collections.FSharpMap`2")!;
         }
 
         private static readonly object Lock = new object();
@@ -133,7 +133,7 @@ namespace Newtonsoft.Json.Utilities
 
         private static MethodInfo GetMethodWithNonPublicFallback(Type type, string methodName, BindingFlags bindingFlags)
         {
-            MethodInfo methodInfo = type.GetMethod(methodName, bindingFlags);
+            MethodInfo methodInfo = type.GetMethod(methodName, bindingFlags)!;
 
             // if no matching method then attempt to find with nonpublic flag
             // this is required because in WinApps some methods are private but always using NonPublic breaks medium trust
@@ -141,7 +141,7 @@ namespace Newtonsoft.Json.Utilities
             // https://github.com/JamesNK/Newtonsoft.Json/issues/821
             if (methodInfo == null && (bindingFlags & BindingFlags.NonPublic) != BindingFlags.NonPublic)
             {
-                methodInfo = type.GetMethod(methodName, bindingFlags | BindingFlags.NonPublic);
+                methodInfo = type.GetMethod(methodName, bindingFlags | BindingFlags.NonPublic)!;
             }
 
             return methodInfo!;
@@ -150,7 +150,7 @@ namespace Newtonsoft.Json.Utilities
         private static MethodCall<object?, object> CreateFSharpFuncCall(Type type, string methodName)
         {
             MethodInfo innerMethodInfo = GetMethodWithNonPublicFallback(type, methodName, BindingFlags.Public | BindingFlags.Static);
-            MethodInfo invokeFunc = innerMethodInfo.ReturnType.GetMethod("Invoke", BindingFlags.Public | BindingFlags.Instance);
+            MethodInfo invokeFunc = innerMethodInfo.ReturnType.GetMethod("Invoke", BindingFlags.Public | BindingFlags.Instance)!;
 
             MethodCall<object?, object?> call = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(innerMethodInfo);
             MethodCall<object?, object> invoke = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object?>(invokeFunc)!;
@@ -175,17 +175,17 @@ namespace Newtonsoft.Json.Utilities
 
         public ObjectConstructor<object> CreateMap(Type keyType, Type valueType)
         {
-            MethodInfo creatorDefinition = typeof(FSharpUtils).GetMethod("BuildMapCreator");
+            MethodInfo creatorDefinition = typeof(FSharpUtils).GetMethod("BuildMapCreator")!;
 
             MethodInfo creatorGeneric = creatorDefinition.MakeGenericMethod(keyType, valueType);
 
-            return (ObjectConstructor<object>)creatorGeneric.Invoke(this, null);
+            return (ObjectConstructor<object>)creatorGeneric.Invoke(this, null)!;
         }
 
         public ObjectConstructor<object> BuildMapCreator<TKey, TValue>()
         {
             Type genericMapType = _mapType.MakeGenericType(typeof(TKey), typeof(TValue));
-            ConstructorInfo ctor = genericMapType.GetConstructor(new[] { typeof(IEnumerable<Tuple<TKey, TValue>>) });
+            ConstructorInfo ctor = genericMapType.GetConstructor(new[] { typeof(IEnumerable<Tuple<TKey, TValue>>) })!;
             ObjectConstructor<object> ctorDelegate = JsonTypeReflector.ReflectionDelegateFactory.CreateParameterizedConstructor(ctor);
 
             ObjectConstructor<object> creator = args =>

Src/Newtonsoft.Json/Utilities/ImmutableCollectionsUtils.cs

@@ -116,17 +116,17 @@ namespace Newtonsoft.Json.Utilities
             if (underlyingType.IsGenericType())
             {
                 Type underlyingTypeDefinition = underlyingType.GetGenericTypeDefinition();
-                string name = underlyingTypeDefinition.FullName;
+                string name = underlyingTypeDefinition.FullName!;
 
-                ImmutableCollectionTypeInfo definition = ArrayContractImmutableCollectionDefinitions.FirstOrDefault(d => d.ContractTypeName == name);
+                ImmutableCollectionTypeInfo? definition = ArrayContractImmutableCollectionDefinitions.FirstOrDefault(d => d.ContractTypeName == name);
                 if (definition != null)
                 {
-                    Type createdTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.CreatedTypeName);
-                    Type builderTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.BuilderTypeName);
+                    Type? createdTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.CreatedTypeName);
+                    Type? builderTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.BuilderTypeName);
 
                     if (createdTypeDefinition != null && builderTypeDefinition != null)
                     {
-                        MethodInfo mb = builderTypeDefinition.GetMethods().FirstOrDefault(m => m.Name == "CreateRange" && m.GetParameters().Length == 1);
+                        MethodInfo? mb = builderTypeDefinition.GetMethods().FirstOrDefault(m => m.Name == "CreateRange" && m.GetParameters().Length == 1);
                         if (mb != null)
                         {
                             createdType = createdTypeDefinition.MakeGenericType(collectionItemType);
@@ -148,17 +148,17 @@ namespace Newtonsoft.Json.Utilities
             if (underlyingType.IsGenericType())
             {
                 Type underlyingTypeDefinition = underlyingType.GetGenericTypeDefinition();
-                string name = underlyingTypeDefinition.FullName;
+                string name = underlyingTypeDefinition.FullName!;
 
-                ImmutableCollectionTypeInfo definition = DictionaryContractImmutableCollectionDefinitions.FirstOrDefault(d => d.ContractTypeName == name);
+                ImmutableCollectionTypeInfo? definition = DictionaryContractImmutableCollectionDefinitions.FirstOrDefault(d => d.ContractTypeName == name);
                 if (definition != null)
                 {
-                    Type createdTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.CreatedTypeName);
-                    Type builderTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.BuilderTypeName);
+                    Type? createdTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.CreatedTypeName);
+                    Type? builderTypeDefinition = underlyingTypeDefinition.Assembly().GetType(definition.BuilderTypeName);
 
                     if (createdTypeDefinition != null && builderTypeDefinition != null)
                     {
-                        MethodInfo mb = builderTypeDefinition.GetMethods().FirstOrDefault(m =>
+                        MethodInfo? mb = builderTypeDefinition.GetMethods().FirstOrDefault(m =>
                         {
                             ParameterInfo[] parameters = m.GetParameters();
 

Src/Newtonsoft.Json/Utilities/JavaScriptUtils.cs

@@ -289,6 +289,7 @@ namespace Newtonsoft.Json.Utilities
                         }
                         else
                         {
+                            MiscellaneousUtils.Assert(writeBuffer != null);
                             writer.Write(writeBuffer, 0, UnicodeTextLength);
                         }
                     }
@@ -386,7 +387,7 @@ namespace Newtonsoft.Json.Utilities
             bool[] charEscapeFlags, StringEscapeHandling stringEscapeHandling, JsonTextWriter client, char[] writeBuffer, CancellationToken cancellationToken)
         {
             Task task = writer.WriteAsync(delimiter, cancellationToken);
-            if (!task.IsCompletedSucessfully())
+            if (!task.IsCompletedSuccessfully())
             {
                 return WriteEscapedJavaScriptStringWithDelimitersAsync(task, writer, s, delimiter, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
             }
@@ -394,7 +395,7 @@ namespace Newtonsoft.Json.Utilities
             if (!StringUtils.IsNullOrEmpty(s))
             {
                 task = WriteEscapedJavaScriptStringWithoutDelimitersAsync(writer, s, charEscapeFlags, stringEscapeHandling, client, writeBuffer, cancellationToken);
-                if (task.IsCompletedSucessfully())
+                if (task.IsCompletedSuccessfully())
                 {
                     return writer.WriteAsync(delimiter, cancellationToken);
                 }

Src/Newtonsoft.Json/Utilities/LateBoundReflectionDelegateFactory.cs

@@ -50,7 +50,7 @@ namespace Newtonsoft.Json.Utilities
                 return a => c.Invoke(a);
             }
 
-            return a => method.Invoke(null, a);
+            return a => method.Invoke(null, a)!;
         }
 
         public override MethodCall<T, object?> CreateMethodCall<T>(MethodBase method)
@@ -71,10 +71,14 @@ namespace Newtonsoft.Json.Utilities
 
             if (type.IsValueType())
             {
-                return () => (T)Activator.CreateInstance(type);
+                return () => (T)Activator.CreateInstance(type)!;
             }
 
-            ConstructorInfo constructorInfo = ReflectionUtils.GetDefaultConstructor(type, true);
+            ConstructorInfo? constructorInfo = ReflectionUtils.GetDefaultConstructor(type, true);
+            if (constructorInfo == null)
+            {
+                throw new InvalidOperationException("Unable to find default constructor for " + type.FullName);
+            }
 
             return () => (T)constructorInfo.Invoke(null);
         }

Src/Newtonsoft.Json/Utilities/MiscellaneousUtils.cs

@@ -92,7 +92,7 @@ namespace Newtonsoft.Json.Utilities
                 return "{null}";
             }
 
-            return (value is string s) ? @"""" + s + @"""" : value!.ToString();
+            return (value is string s) ? @"""" + s + @"""" : value!.ToString()!;
         }
 
         public static int ByteArrayCompare(byte[] a1, byte[] a2)
@@ -131,7 +131,7 @@ namespace Newtonsoft.Json.Utilities
 
         public static void GetQualifiedNameParts(string qualifiedName, out string? prefix, out string localName)
         {
-            int colonPosition = qualifiedName.IndexOf(':');
+            int colonPosition = StringUtils.IndexOf(qualifiedName, ':');
 
             if ((colonPosition == -1 || colonPosition == 0) || (qualifiedName.Length - 1) == colonPosition)
             {

Src/Newtonsoft.Json/Utilities/NullableAttributes.cs

@@ -23,6 +23,8 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 #endregion
 
+#if !HAVE_NULLABLE_ATTRIBUTES
+
 namespace System.Diagnostics.CodeAnalysis
 {
     /// <summary>Specifies that an output will not be null even if the corresponding type allows it.</summary>
@@ -71,4 +73,6 @@ namespace System.Diagnostics.CodeAnalysis
         /// <summary>Gets the condition parameter value.</summary>
         public bool ParameterValue { get; }
     }
-}
+}
+
+#endif

Src/Newtonsoft.Json/Utilities/ReflectionUtils.cs

@@ -177,7 +177,7 @@ namespace Newtonsoft.Json.Utilities
                 return typeName + (assemblyName == null ? "" : ", " + assemblyName);
             }
 
-            return t.AssemblyQualifiedName;
+            return t.AssemblyQualifiedName!;
         }
 
         private static string RemoveAssemblyDetails(string fullyQualifiedTypeName)
@@ -245,12 +245,12 @@ namespace Newtonsoft.Json.Utilities
             return (GetDefaultConstructor(t, nonPublic) != null);
         }
 
-        public static ConstructorInfo GetDefaultConstructor(Type t)
+        public static ConstructorInfo? GetDefaultConstructor(Type t)
         {
             return GetDefaultConstructor(t, false);
         }
 
-        public static ConstructorInfo GetDefaultConstructor(Type t, bool nonPublic)
+        public static ConstructorInfo? GetDefaultConstructor(Type t, bool nonPublic)
         {
             BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.Public;
             if (nonPublic)
@@ -283,14 +283,14 @@ namespace Newtonsoft.Json.Utilities
         public static Type EnsureNotNullableType(Type t)
         {
             return (IsNullableType(t))
-                ? Nullable.GetUnderlyingType(t)
+                ? Nullable.GetUnderlyingType(t)!
                 : t;
         }
 
         public static Type EnsureNotByRefType(Type t)
         {
             return (t.IsByRef && t.HasElementType)
-                ? t.GetElementType()
+                ? t.GetElementType()!
                 : t;
         }
 
@@ -370,8 +370,9 @@ namespace Newtonsoft.Json.Utilities
             return InheritsGenericDefinitionInternal(type, genericClassDefinition, out implementingType);
         }
 
-        private static bool InheritsGenericDefinitionInternal(Type currentType, Type genericClassDefinition, out Type? implementingType)
+        private static bool InheritsGenericDefinitionInternal(Type type, Type genericClassDefinition, out Type? implementingType)
         {
+            Type? currentType = type;
             do
             {
                 if (currentType.IsGenericType() && genericClassDefinition == currentType.GetGenericTypeDefinition())
@@ -461,7 +462,7 @@ namespace Newtonsoft.Json.Utilities
                 case MemberTypes.Property:
                     return ((PropertyInfo)member).PropertyType;
                 case MemberTypes.Event:
-                    return ((EventInfo)member).EventHandlerType;
+                    return ((EventInfo)member).EventHandlerType!;
                 case MemberTypes.Method:
                     return ((MethodInfo)member).ReturnType;
                 default:
@@ -509,7 +510,7 @@ namespace Newtonsoft.Json.Utilities
         /// <param name="member">The member.</param>
         /// <param name="target">The target object.</param>
         /// <returns>The member's value on the object.</returns>
-        public static object GetMemberValue(MemberInfo member, object target)
+        public static object? GetMemberValue(MemberInfo member, object target)
         {
             ValidationUtils.ArgumentNotNull(member, nameof(member));
             ValidationUtils.ArgumentNotNull(target, nameof(target));
@@ -713,7 +714,7 @@ namespace Newtonsoft.Json.Utilities
                 return false;
             }
 
-            Type declaringType = propertyInfo.DeclaringType;
+            Type declaringType = propertyInfo.DeclaringType!;
             if (!declaringType.IsGenericType())
             {
                 return false;
@@ -884,7 +885,7 @@ namespace Newtonsoft.Json.Utilities
             return null;
         }
 
-        public static MemberInfo GetMemberInfoFromType(Type targetType, MemberInfo memberInfo)
+        public static MemberInfo? GetMemberInfoFromType(Type targetType, MemberInfo memberInfo)
         {
             const BindingFlags bindingAttr = BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic;
 
@@ -916,8 +917,10 @@ namespace Newtonsoft.Json.Utilities
         }
 
 #if !PORTABLE
-        private static void GetChildPrivateFields(IList<MemberInfo> initialFields, Type targetType, BindingFlags bindingAttr)
+        private static void GetChildPrivateFields(IList<MemberInfo> initialFields, Type type, BindingFlags bindingAttr)
         {
+            Type? targetType = type;
+
             // fix weirdness with private FieldInfos only being returned for the current Type
             // find base type fields and add them to result
             if ((bindingAttr & BindingFlags.NonPublic) != 0)
@@ -960,7 +963,7 @@ namespace Newtonsoft.Json.Utilities
                 PropertyInfo member = propertyInfos[i];
                 if (member.DeclaringType != targetType)
                 {
-                    PropertyInfo declaredMember = (PropertyInfo)GetMemberInfoFromType(member.DeclaringType, member);
+                    PropertyInfo declaredMember = (PropertyInfo)GetMemberInfoFromType(member.DeclaringType!, member)!;
                     propertyInfos[i] = declaredMember;
                 }
             }
@@ -975,13 +978,14 @@ namespace Newtonsoft.Json.Utilities
                 : bindingAttr;
         }
 
-        private static void GetChildPrivateProperties(IList<PropertyInfo> initialProperties, Type targetType, BindingFlags bindingAttr)
+        private static void GetChildPrivateProperties(IList<PropertyInfo> initialProperties, Type type, BindingFlags bindingAttr)
         {
             // fix weirdness with private PropertyInfos only being returned for the current Type
             // find base type properties and add them to result
 
             // also find base properties that have been hidden by subtype properties with the same name
 
+            Type? targetType = type;
             while ((targetType = targetType.BaseType()) != null)
             {
                 foreach (PropertyInfo propertyInfo in targetType.GetProperties(bindingAttr))
@@ -1025,11 +1029,11 @@ namespace Newtonsoft.Json.Utilities
                     }
                     else
                     {
-                        Type subTypePropertyDeclaringType = subTypeProperty.GetBaseDefinition()?.DeclaringType ?? subTypeProperty.DeclaringType;
+                        Type subTypePropertyDeclaringType = subTypeProperty.GetBaseDefinition()?.DeclaringType ?? subTypeProperty.DeclaringType!;
 
                         int index = initialProperties.IndexOf(p => p.Name == subTypeProperty.Name
                                                                    && p.IsVirtual()
-                                                                   && (p.GetBaseDefinition()?.DeclaringType ?? p.DeclaringType).IsAssignableFrom(subTypePropertyDeclaringType));
+                                                                   && (p.GetBaseDefinition()?.DeclaringType ?? p.DeclaringType!).IsAssignableFrom(subTypePropertyDeclaringType));
 
                         // don't add a virtual property that has an override
                         if (index == -1)

Src/Newtonsoft.Json/Utilities/StringBuffer.cs

@@ -107,7 +107,7 @@ namespace Newtonsoft.Json.Utilities
 
         public string ToString(int start, int length)
         {
-            // TODO: validation
+            MiscellaneousUtils.Assert(_buffer != null);
             return new string(_buffer, start, length);
         }
 

Src/Newtonsoft.Json/Utilities/StringUtils.cs

@@ -128,7 +128,7 @@ namespace Newtonsoft.Json.Utilities
             buffer[5] = MathUtils.IntToHex(c & '\x000f');
         }
 
-        public static TSource ForgivingCaseSensitiveFind<TSource>(this IEnumerable<TSource> source, Func<TSource, string> valueSelector, string testValue)
+        public static TSource? ForgivingCaseSensitiveFind<TSource>(this IEnumerable<TSource> source, Func<TSource, string> valueSelector, string testValue)
         {
             if (source == null)
             {
@@ -303,6 +303,24 @@ namespace Newtonsoft.Json.Utilities
 #endif
         }
 
+        public static int IndexOf(string s, char c)
+        {
+#if HAVE_INDEXOF_STRING_COMPARISON
+            return s.IndexOf(c, StringComparison.Ordinal);
+#else
+            return s.IndexOf(c);
+#endif
+        }
+
+        public static string Replace(string s, string oldValue, string newValue)
+        {
+#if HAVE_REPLACE_STRING_COMPARISON
+            return s.Replace(oldValue, newValue, StringComparison.Ordinal);
+#else
+            return s.Replace(oldValue, newValue);
+#endif
+        }
+
         public static bool StartsWith(this string source, char value)
         {
             return (source.Length > 0 && source[0] == value);

Src/Newtonsoft.Json/Utilities/StructMultiKey.cs

@@ -43,7 +43,7 @@ namespace Newtonsoft.Json.Utilities
             return (Value1?.GetHashCode() ?? 0) ^ (Value2?.GetHashCode() ?? 0);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (!(obj is StructMultiKey<T1, T2> key))
             {

Src/Newtonsoft.Json/Utilities/ThreadSafeStore.cs

@@ -36,7 +36,7 @@ using Newtonsoft.Json.Serialization;
 
 namespace Newtonsoft.Json.Utilities
 {
-    internal class ThreadSafeStore<TKey, TValue>
+    internal class ThreadSafeStore<TKey, TValue> where TKey : notnull
     {
 #if HAVE_CONCURRENT_DICTIONARY
         private readonly ConcurrentDictionary<TKey, TValue> _concurrentStore;

Src/Newtonsoft.Json/Utilities/TypeExtensions.cs

@@ -171,7 +171,7 @@ namespace Newtonsoft.Json.Utilities
 #endif
         }
 
-        public static Type BaseType(this Type type)
+        public static Type? BaseType(this Type type)
         {
 #if HAVE_FULL_REFLECTION
             return type.BaseType;
@@ -580,7 +580,7 @@ namespace Newtonsoft.Json.Utilities
 
         public static bool AssignableToTypeName(this Type type, string fullTypeName, bool searchInterfaces, [NotNullWhen(true)]out Type? match)
         {
-            Type current = type;
+            Type? current = type;
 
             while (current != null)
             {
@@ -616,7 +616,7 @@ namespace Newtonsoft.Json.Utilities
 
         public static bool ImplementInterface(this Type type, Type interfaceType)
         {
-            for (Type currentType = type; currentType != null; currentType = currentType.BaseType())
+            for (Type? currentType = type; currentType != null; currentType = currentType.BaseType())
             {
                 IEnumerable<Type> interfaces = currentType.GetInterfaces();
                 foreach (Type i in interfaces)