Index: src/Galaxium.Core/Utilities/ArgumentUtility.cs
===================================================================
--- src/Galaxium.Core/Utilities/ArgumentUtility.cs	(revision 1217)
+++ src/Galaxium.Core/Utilities/ArgumentUtility.cs	(revision 1218)
@@ -278,10 +278,10 @@
 		/// <returns></returns>
 		public static bool IsNullable (object obj)
 		{
-			if (obj == null)
-				return false;
+			var type = obj.GetType ();
 
-			return obj is Nullable;
+			return (type.IsGenericType
+			        && type.GetGenericTypeDefinition ().Equals (typeof (Nullable<>)));
 		}
 
 		/// <summary>