Memory management question

1

If I have something like this:


package {
   import flash.display.Sprite;

   public class Car extends Sprite {
      private var _engine:Sprite;

      public function Car(engine:Sprite = null) {
         this.engine = engine;
      }

      public function set engine(engine:Sprite):void {
         if(_engine) {
            removeChild(_engine);
         }

         //_engine = null;
         _engine = engine;
         addChild(_engine);
      }
   }
}

is it necessary to put

_engine = null;

right before

_engine = engine;

?