public static function getByID($pkID)
    {
        $keys = null;
        $app = Application::getFacadeApplication();
        $cache = $app->make('cache/request');
        if ($cache->isEnabled()) {
            $item = $cache->getItem('permission_keys');
            if (!$item->isMiss()) {
                $keys = $item->get();
            }
        }
        if ($keys === null) {
            $keys = self::loadAll();
        }

        return isset($keys[$pkID]) ? $keys[$pkID] : null;
    }