     // from interface OccupantObserver
     public function occupantEntered (info :OccupantInfo) :void
     {
-        if (_entered) {
+        if (_entered != null) {
             _entered(info);
         }
     }

    // from interface OccupantObserver
    public function occupantUpdated (oldinfo :OccupantInfo, newinfo :OccupantInfo) :void
    {
        if (_updated) {
            _updated(oldinfo, newinfo);
        }
    }

    // from interface OccupantObserver
    public function occupantLeft (info :OccupantInfo) :void
    {
        if (_left != null) {
            _left(info);
        }
    }
