Проблема при создании Button

[alekson]

        private function setupButtons():void {
            b1 = new Button();

            b1.width = 160;

            b1.move(10,10);

            b1.label = "Default Button";

           
            b1.addEventListener(MouseEvent.CLICK, buttonClick);
			
			trace(b1);

            parentObject.addChild(b1);
        }

trace

[object Button]
TypeError: Error #2007: Parameter child must be non-null.
	at flash.display::DisplayObjectContainer/addChildAt()
	at fl.controls::BaseButton/fl.controls:BaseButton::drawBackground()
	at fl.controls::LabelButton/fl.controls:LabelButton::draw()
	at fl.controls::Button/fl.controls:Button::draw()
	at fl.core::UIComponent/::callLaterDispatcher()

почему null то?