Add fix for deserializing nullable enums

Author: mythz

src/ServiceStack.Text/Common/ParseUtils.cs

@@ -63,6 +63,9 @@ public static Type ParseType(string assemblyQualifiedName)
 
         public static object TryParseEnum(Type enumType, string str)
         {
+            if (str == null)
+                return null;
+
             if (JsConfig.EmitLowercaseUnderscoreNames)
             {
                 string[] names = Enum.GetNames(enumType);

tests/ServiceStack.Text.Tests/EnumTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.Serialization;
 using NUnit.Framework;
 
 namespace ServiceStack.Text.Tests
@@ -157,6 +158,25 @@ public void Can_serialize_different_enum_styles()
                 Assert.That("Underscore_Words".FromJson<EnumStyles>(), Is.EqualTo(EnumStyles.Underscore_Words));
             }
         }
+
+        [DataContract]
+        public class NullableEnum
+        {
+            [DataMember(Name = "myEnum")]
+            public EnumWithoutFlags? MyEnum { get; set; }
+        }
+
+        [Test]
+        public void Can_deserialize_null_Nullable_Enum()
+        {
+            JsConfig.ThrowOnDeserializationError = true;
+            string json = @"{""myEnum"":null}";
+            var o = json.FromJson<NullableEnum>();
+            Assert.That(o.MyEnum, Is.Null);
+
+            JsConfig.Reset();
+        }
+
     }
 }