-Changed $id and $ref properties to allow null

Src/Newtonsoft.Json.Tests/Properties/AssemblyInfo.cs

@@ -41,5 +41,5 @@ using System.Runtime.InteropServices;
 // by using the '*' as shown below:
 [assembly: AssemblyVersion("4.0.2.0")]
 #if !PocketPC
-[assembly: AssemblyFileVersion("4.0.2.13928")]
+[assembly: AssemblyFileVersion("4.0.2.14001")]
 #endif

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

@@ -3272,7 +3272,7 @@ keyword such as type of business.""
     }
 
     [Test]
-    [ExpectedException(typeof(JsonSerializationException), ExpectedMessage = "JSON reference $ref property must have a string value.")]
+    [ExpectedException(typeof(JsonSerializationException), ExpectedMessage = "JSON reference $ref property must have a string or null value.")]
     public void SerializeRefBadType()
     {
       //Additional text found in JSON string after finishing deserializing object.
@@ -3290,6 +3290,27 @@ keyword such as type of business.""
       JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
     }
 
+    [Test]
+    public void SerializeRefNull()
+    {
+      var reference = new Dictionary<string, object>();
+      reference.Add("$ref", null);
+      reference.Add("$id", null);
+      reference.Add("blah", "blah!");
+
+      var child = new Dictionary<string, object>();
+      child.Add("_id", 2);
+      child.Add("Name", "Isabell");
+      child.Add("Father", reference);
+
+      var json = JsonConvert.SerializeObject(child);
+      Dictionary<string, object> result = JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
+
+      Assert.AreEqual(3, result.Count);
+      Assert.AreEqual(1, ((JObject) result["Father"]).Count);
+      Assert.AreEqual("blah!", (string)((JObject)result["Father"])["blah"]);
+    }
+
     public class ConstructorCompexIgnoredProperty
     {
       [JsonIgnore]

Src/Newtonsoft.Json/Properties/AssemblyInfo.cs

@@ -110,7 +110,7 @@ using System.Security;
 // by using the '*' as shown below:
 [assembly: AssemblyVersion("4.0.2.0")]
 #if !PocketPC
-[assembly: AssemblyFileVersion("4.0.2.13928")]
+[assembly: AssemblyFileVersion("4.0.2.14001")]
 #endif
 
 [assembly: CLSCompliant(true)]

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs

@@ -77,7 +77,7 @@ namespace Newtonsoft.Json.Serialization
         if (reader.TokenType == JsonToken.PropertyName && string.Equals(reader.Value.ToString(), JsonTypeReflector.IdPropertyName, StringComparison.Ordinal))
         {
           CheckedRead(reader);
-          id = reader.Value.ToString();
+          id = (reader.Value != null) ? reader.Value.ToString() : null;
           CheckedRead(reader);
         }
 
@@ -307,16 +307,24 @@ namespace Newtonsoft.Json.Serialization
           if (string.Equals(propertyName, JsonTypeReflector.RefPropertyName, StringComparison.Ordinal))
           {
             CheckedRead(reader);
-            if (reader.TokenType != JsonToken.String)
-              throw new JsonSerializationException("JSON reference {0} property must have a string value.".FormatWith(CultureInfo.InvariantCulture, JsonTypeReflector.RefPropertyName));
+            if (reader.TokenType != JsonToken.String && reader.TokenType != JsonToken.Null)
+              throw new JsonSerializationException("JSON reference {0} property must have a string or null value.".FormatWith(CultureInfo.InvariantCulture, JsonTypeReflector.RefPropertyName));
 
-            string reference = reader.Value.ToString();
+            string reference = (reader.Value != null) ? reader.Value.ToString() : null;
 
             CheckedRead(reader);
-            if (reader.TokenType == JsonToken.PropertyName)
-              throw new JsonSerializationException("Additional content found in JSON reference object. A JSON reference object should only have a {0} property.".FormatWith(CultureInfo.InvariantCulture, JsonTypeReflector.RefPropertyName));
 
-            return Serializer.ReferenceResolver.ResolveReference(this, reference);
+            if (reference != null)
+            {
+              if (reader.TokenType == JsonToken.PropertyName)
+                throw new JsonSerializationException("Additional content found in JSON reference object. A JSON reference object should only have a {0} property.".FormatWith(CultureInfo.InvariantCulture, JsonTypeReflector.RefPropertyName));
+
+              return Serializer.ReferenceResolver.ResolveReference(this, reference);
+            }
+            else
+            {
+              specialProperty = true;
+            }
           }
           else if (string.Equals(propertyName, JsonTypeReflector.TypePropertyName, StringComparison.Ordinal))
           {
@@ -356,7 +364,8 @@ namespace Newtonsoft.Json.Serialization
           {
             CheckedRead(reader);
 
-            id = reader.Value.ToString();
+            id = (reader.Value != null) ? reader.Value.ToString() : null;
+
             CheckedRead(reader);
             specialProperty = true;
           }