protected function saveAllKeywordsToFiles($lastUpdate = null)
    {
        if ($lastUpdate === null) {
            $lastUpdate = time();
        }

        $this->saveKeywordsToFile($this->whitelist, $this->whitelistCacheFilePath, $lastUpdate);
        $this->saveKeywordsToFile($this->blacklist, $this->blacklistCacheFilePath, $lastUpdate);
    }