Fix JsonObject null response

Author: mythz

src/ServiceStack.Text/Common/DeserializeDictionary.cs

@@ -85,6 +85,9 @@ public static ParseStringSegmentDelegate GetParseStringSegmentMethod(Type type)
 
         public static JsonObject ParseJsonObject(StringSegment value)
         {
+            if (value.Length == 0)
+                return null;
+
             var index = VerifyAndGetStartIndex(value, typeof(JsonObject));
 
             var result = new JsonObject();
@@ -270,7 +273,7 @@ public static IDictionary<TKey, TValue> ParseDictionary<TKey, TValue>(
         private static int VerifyAndGetStartIndex(StringSegment value, Type createMapType)
         {
             var index = 0;
-            if (!Serializer.EatMapStartChar(value, ref index))
+            if (value.Length > 0 && !Serializer.EatMapStartChar(value, ref index))
             {
                 //Don't throw ex because some KeyValueDataContractDeserializer don't have '{}'
                 Tracer.Instance.WriteDebug("WARN: Map definitions should start with a '{0}', expecting serialized type '{1}', got string starting with: {2}",

tests/ServiceStack.Text.Tests/JsonTests/JsonObjectTests.cs

@@ -26,6 +26,22 @@ public void Can_parse_empty_object_with_mixed_whitespaces()
             Assert.That(JsonObject.Parse("{ \n\t  \n\r}"), Is.Empty);
         }
 
+
+        public class JsonObjectResponse
+        {
+            public JsonObject result { get; set; }
+        }
+
+        [Test]
+        public void Can_serialize_null_JsonObject_response()
+        {
+            JsConfig.ThrowOnDeserializationError = true;
+            var json = "{\"result\":null}";
+            var dto = json.FromJson<JsonObjectResponse>();
+            Assert.That(dto.result, Is.Null);
+            JsConfig.ThrowOnDeserializationError = false;
+        }
+
         [Test]
         public void Can_Serialize_numbers()
         {