Flash Game hitTestObject Error

Question

I'm new to ActionScript but I've been following Lynda tutorials and  tried to tailor them to my game. I simply want to make my character at  the top of the screen shoot at enemies below. The error I'm getting when  I press the shoot button is "Parameter hitTestObject must be non-null." I've read some other forum posts on this error for ideas but still can't seem to make mine work.
package
     import flash.display.MovieClip;
     import flash.events.Event;
     public class Bullet extends MovieClip
          var enemyRobber:MovieClip;
          var ySpeed:Number;
          public var speed:Number;
          var thisBullet:MovieClip;
          var floor:MovieClip;
          var thisParent:*;
          public function Bullet(enemy:MovieClip)
               speed = 20;
               enemyRobber = enemy;
               this.addEventListener(Event.ADDED, initialize)
          function initialize(event:Event):void
               thisParent = event.currentTarget.parent;
               floor = thisParent.floor_mc;
               thisBullet = MovieClip(this.parent.getChildByName(this.name));
               ySpeed = speed;
               this.addEventListener(Event.ENTER_FRAME, moveBullet);
          function moveBullet(event:Event):void
               if(this.hitTestObject(enemyRobber))
                    this.removeEventListener(Event.ENTER_FRAME, moveBullet);
                    this.parent.removeChild(thisBullet);
               else if(this.hitTestObject(floor))
                    this.removeEventListener(Event.ENTER_FRAME, moveBullet);
                    this.parent.removeChild(thisBullet);
               else
                    this.y += ySpeed;

Answer 1

Go into your Flash Publish Settings and select the option to Permit Debugging.  What that should do is add a line number to the error message so that you can see whether the enemy or the floor is not being seen for that hitTestObject method call.