Error #1009: Driving me crazy

programming flash
1

It’s me again, my game is giving me some problems. Basically, I moved all the “game code” into a MovieClip called “PlayScreen” (previously “FightingGame”). Then I created a new DocumentClass file and set it as the Document Class. for some reason, when trying to add a child its basically saying that the object is null, though I have no idea why.
line 32 for “FightingGame” @ stage.AddEventListener
line 9 for “DocumentClass” @ addCHild

TypeError: Error #1009: Cannot access a property or method of a null object reference.

The code in the DocumentClass: set as DocumentClass.

package
{
	import flash.display.MovieClip;
	import flash.events.Event;
	
   public class DocumentClass extends MovieClip
   {
      //New Constructor
	  public var playscreen:FightingGame = new FightingGame;
      public function DocumentClass()
      {
         addEventListener(Event.ADDED_TO_STAGE, FightingGameBuild, false, 0, true);
      }
      //Old Constructor
      public function FightingGameBuild(event:Event):void
      {
         removeEventListener(Event.ADDED_TO_STAGE, FightingGameBuild);
		 trace("new constructor");
		 addChild(playscreen);
		
		
		
         
      }
   }
}

Here is the relevant part of the FightingGame Code:

public function FightingGame() {
			buildLevel();
			stage.addEventListener(KeyboardEvent.KEY_DOWN,keydownlistener);
			stage.addEventListener(KeyboardEvent.KEY_UP,keyuplistener);
			gametimer = new Timer(25);
			gametimer.addEventListener(TimerEvent.TIMER,Update);
			gametimer.start();