private function cacheIsset($keys)
    {
        $has   = false;
        $array = $this->cache;

        foreach ($keys as $key) {
            if ($has = array_key_exists($key, $array)) {
                $array = $array[$key];
            }
        }

        if (is_array($array)) {
            $has = $has && array_key_exists(0, $array);
        }

        return $has;
    }