An exception for non-default arg prior to WillReturn()

Please make Isolator throw an exception for Isolate.WhenCalled(() => obj.Method(arg)).WillReturn(returnValue) when arg != default(typeof(arg)).

Currently I find it easy to misinterpret
Isolate.WhenCalled(() => obj.Method(1)).WillReturn(1)
as being
Isolate.WhenCalled(() => a.Method(1)).WithExactArguments().WillReturn(1).