Add IsDefaultValue Utils

Author: mythz

src/ServiceStack.Text/AutoMappingUtils.cs

@@ -416,7 +416,8 @@ private static object PopulateObjectInternal(object obj, Dictionary<Type, int> r
 
         public static object GetDefaultValue(this Type type)
         {
-            if (!type.IsValueType) return null;
+            if (!type.IsValueType) 
+                return null;
 
             if (DefaultValueTypes.TryGetValue(type, out var defaultValue))
                 return defaultValue;
@@ -435,6 +436,10 @@ public static object GetDefaultValue(this Type type)
             return defaultValue;
         }
 
+        public static bool IsDefaultValue(object value) => IsDefaultValue(value, value?.GetType());
+        public static bool IsDefaultValue(object value, Type valueType) => value == null 
+            || (valueType.IsValueType && value.Equals(valueType.GetDefaultValue()));
+
         private static readonly ConcurrentDictionary<string, AssignmentDefinition> AssignmentDefinitionCache
             = new ConcurrentDictionary<string, AssignmentDefinition>();