protected function putCacheIndex($cacheKey)
    {
        $index = [];

        if (Cache::has('combiner.index')) {
            $index = (array) @unserialize(@base64_decode(Cache::get('combiner.index'))) ?: [];
        }

        if (in_array($cacheKey, $index)) {
            return false;
        }

        $index[] = $cacheKey;

        Cache::forever('combiner.index', base64_encode(serialize($index)));

        return true;
    }