protected function initializeMenu($instance = null) {
        $menu = null;
        if (null == $instance) {
            $instance = $this->getInstance();
        }
        $theme_info = self::$themes[$instance['theme']];
        $theme = new $theme_info['class'];
 
        $menu = new GantryMenu($theme, $instance);
        $menu->initialize();
        return $menu;
    }