Null object reference

1

i have this class

package {
    import flash.display.*;
    import flash.events.Event;
    import flash.net.URLRequest;

    public class Fullscreen extends Sprite {

        private var _bg:Sprite = new Sprite(), _loader:Loader = new Loader(), url:String, _req:URLRequest;

        public function Fullscreen(str:String):void {
            addChild(_bg);
            trace(str);
            url = str;
            _req = new URLRequest(url);
            _loader.load(_req);
            _loader.contentLoaderInfo.addEventListener(Event.COMPLETE, imgLoaded);
        }
        
        private function onStageResize(... eventArray:Array):void {
            _bgresize();
        }
        
        private function imgLoaded(evt:Event):void {
            stage.frameRate = 32;
            stage.showDefaultContextMenu = false;
            stage.scaleMode = StageScaleMode.NO_SCALE;
            stage.align = StageAlign.TOP_LEFT;
            stage.addEventListener(Event.RESIZE,onStageResize);
            _bg.addChild(_loader.content);
            _bgresize();
        }
        
        private function _bgresize():void {
            _bg.width = (stage.height/stage.width > _bg.height/_bg.width) ? stage.stageHeight*(_bg.width/_bg.height) : stage.stageWidth;
            _bg.height = (stage.height/stage.width > _bg.height/_bg.width) ? stage.stageHeight : stage.stageWidth*(_bg.height/_bg.width);
        }
    }
}

and it’s outputting this error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Fullscreen/::imgLoaded()

i’m pretty sure the stage values are null, but i dont know why. any ideas?