-Fixed deserializing a null string throwing a NullReferenceException

-Fixed JsonTextReader reading from a slow stream
-Fixed CultureInfo not being overridden on JsonSerializerProxy
-Fixed full trust security check in .NET 2.0 & .NET 3.5
-Improved writing JSON with indent performance

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs

@@ -117,7 +117,7 @@ namespace Newtonsoft.Json.Serialization
 
       if (reader.TokenType == JsonToken.None && !ReadForType(reader, contract, converter != null, false))
       {
-        if (!contract.IsNullable)
+        if (contract != null && !contract.IsNullable)
           throw new JsonSerializationException("No JSON content found and type '{0}' is not nullable.".FormatWith(CultureInfo.InvariantCulture, contract.UnderlyingType));
 
         return null;