static public function getInstance($storagePath = null) {
        if (!self::$_instance) {
            if (empty($storagePath)) {
                throw new \Exception("Storage path need to be specified on the first instance call for ModelOperator");
            }
            self::$_instance = new ModelOperator($storagePath);
            self::$_instance->loadStructureFiles();
        }
        return self::$_instance;
    }