Class内でstageプロパティがnullになる

package  {
	import flash.display.MovieClip;
	import flash.events.Event;
	public class SomeClass extends MovieClip {
		public function SomeClass(){
			super();
			addEventListener(Event.ADDED_TO_STAGE, init);
		}
		private function init(evt:Event) : void {
			removeEventListener(Event.ADDED_TO_STAGE, init);
			trace (stage.stageWidth);
		}
	}	
}