private function getWalker(ReplaceInsertTagsEvent $event)
    {
        $identifier = $event->getParam(0);

        if (!isset(static::$walkers[$identifier])) {
            list($columnSetId, $infinite) = $this->translateParams($event);

            try {
                static::$walkers[$identifier] = new Walker(Factory::createById($columnSetId), false, $infinite);
            } catch (\Exception $e) {
                return null;
            }
        }

        return static::$walkers[$identifier];
    }