protected function getCache($sKey, $bReturnValue = true)
    {
        if (!static::$CACHING_ENABLED) {
            return false;
        } elseif (empty($sKey)) {
            return false;
        }

        $sCacheKey = $this->getCachePrefix() . $sKey;
        foreach ($this->aCache as $iIndex => $oCacheItem) {
            if (in_array($sCacheKey, $oCacheItem->key)) {
                return $bReturnValue ? $oCacheItem->value : $iIndex;
            }
        }

        return null;
    }