Stops including the typename for nullable structs using TypeNameHandling.Auto, fixes #1050

Src/Newtonsoft.Json.Tests/Serialization/TypeNameHandlingTests.cs

@@ -1934,9 +1934,50 @@ namespace Newtonsoft.Json.Tests.Serialization
 
             Assert.IsNotNull(obtainedDictionary);
         }
+
+        [Test]
+        public void SerializeNullableStructProperty_Auto()
+        {
+            ObjectWithOptionalMessage objWithMessage = new ObjectWithOptionalMessage(new Message2("Hello!"));
+
+            JsonSerializerSettings serializerSettings = new JsonSerializerSettings
+            {
+                TypeNameHandling = TypeNameHandling.Auto,
+                Formatting = Formatting.Indented
+            };
+
+            StringAssert.AreEqual(@"{
+  ""Message"": {
+    ""Value"": ""Hello!""
+  }
+}", JsonConvert.SerializeObject(objWithMessage, serializerSettings));
+        }
 #endif
     }
 
+    public struct Message2
+    {
+        public string Value { get; }
+
+        [JsonConstructor]
+        public Message2(string value)
+        {
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
+            Value = value;
+        }
+    }
+
+    public class ObjectWithOptionalMessage
+    {
+        public Message2? Message { get; }
+
+        public ObjectWithOptionalMessage(Message2? message)
+        {
+            Message = message;
+        }
+    }
+
     public class DataType
     {
         public DataType()

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs

@@ -1002,14 +1002,14 @@ namespace Newtonsoft.Json.Serialization
             {
                 if (member != null)
                 {
-                    if (contract.UnderlyingType != member.PropertyContract.CreatedType)
+                    if (contract.NonNullableUnderlyingType != member.PropertyContract.CreatedType)
                     {
                         return true;
                     }
                 }
                 else if (containerContract != null)
                 {
-                    if (containerContract.ItemContract == null || contract.UnderlyingType != containerContract.ItemContract.CreatedType)
+                    if (containerContract.ItemContract == null || contract.NonNullableUnderlyingType != containerContract.ItemContract.CreatedType)
                     {
                         return true;
                     }
@@ -1018,7 +1018,7 @@ namespace Newtonsoft.Json.Serialization
                 {
                     JsonContract rootContract = Serializer._contractResolver.ResolveContract(_rootType);
 
-                    if (contract.UnderlyingType != rootContract.CreatedType)
+                    if (contract.NonNullableUnderlyingType != rootContract.CreatedType)
                     {
                         return true;
                     }