public function getFromCache($key)
    {
        $fileName = $this->getCacheFilePath($key);
        $value = null;
        if (is_readable($fileName)) {
            $value = file_get_contents($fileName);
            if ($value == serialize(false)) {
                return false;
            }

            $value = unserialize($value);
            if ($value === false) {
                $value = null;
            }
        }

        return $value;
    }