/**
  * returns the specific model
  *
  * @param $id_game int
  * @param $id_game_area int
  * @throws NullPointerException
  * @return ModelGameArea
  */
 public static function getGameArea($id_game, $id_game_area)
 {
     $id_game = intval($id_game);
     $id_game_area = intval($id_game_area);
     if (isset(self::$game_areas[$id_game][$id_game_area])) {
         return self::$game_areas[$id_game][$id_game_area];
     }
     $area = new ModelGameArea($id_game, $id_game_area);
     self::$game_areas[$id_game][$id_game_area] = $area;
     self::$game_areas_for_area[$id_game][$area->getIdArea()] = $area;
     return $area;
 }