protected function isCachedByString($string, int $siteId = null)
    {

        // Resolve siteId
        $siteId = SiteHelper::resolveSiteId($siteId);

        if (!isset($this->cacheByString[$siteId])) {
            $this->cacheByString[$siteId] = [];
        }

        return array_key_exists($string, $this->cacheByString[$siteId]);
    }