Loading External Swf in Movie Clip

programming flash
1

Need some help in loading external swf using AS 3.0

I am using the below code

var swfLoader:Loader = new Loader();
holderMC.addChild(swfLoader);
var bgURL:URLRequest=new URLRequest("Untitled-1.swf");
swfLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadProdComplete);
swfLoader.load(bgURL);
function loadProdComplete(e:Event):void {
    trace("file loaded");
}

and it is showing the error
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Untitled_fla::MainTimeline/frame1()

Can anyone help me in fixing this error…