Calling Sequence in Atlas

I just tried something new in Atlas.  Let's say that I want to specify a callback on completion and a callback on an exception on the server, but not a callback on a ServerTimeOut.  Its as easy as I thought.  This code seems to do it.  Passing a null to the callback method parameter seems to work correctly.  If you have an suggestions, let me know.

    function EventMethod()
    {
        WebServiceTest.GetProjects(MethodReturn, null, OnServerError);
    }
    function MethodReturn(result)
    {
        debug.dump(result,"Result Returned");
        alert("Done");
    }
    function OnServerError(result)
    {
        alert("Error on the server.")
    }