Getting more debug info on what code created an async callback

gistfile1.as

package
{
    import flash.events.TimerEvent;
    import flash.utils.Timer;

    public class TestClass
    {
        public function TestClass(userCallback:Function)
        {
            var errorInConsumerScope:Error = new Error()
            
            var timer:Timer = new Timer(1000, 1)
            timer.addEventListener(TimerEvent.TIMER, internalCallback)
            timer.start()
            
            function internalCallback(e:TimerEvent):void 
            {
                try
                {
                    var nullProperty:String
                    nullProperty.length
                    userCallback()
                }
                catch (e:Error)
                {
                    errorInConsumerScope.message = e.message
                    throw errorInConsumerScope
                }
            }
        }
    }
}

package
{
    import flash.display.Sprite;
    
    public class Main extends Sprite
    {
        public function Main()
        {
            new TestClass(function ():void {
                trace('call me back when your done')
            })
        }   
    }
}

/*
Error: Error #1009: Cannot access a property or method of a null object reference.
	at TestClass()[/[path-to-source-file]/TestClass.as:10]
	at Main()[/[path-to-source-file]/Main.as:9]
*/