protected function getServiceKeys($pattern = null)
    {
        $keys = $this->getKeys();
        $serviceKey = $this->getCacheKey();
        $serviceKeys = isset($keys[$serviceKey]) ? $keys[$serviceKey] : [];

        if (!is_null($pattern)) {
            $serviceKeys = $this->filterArrayValuesWithPattern(
                $serviceKeys,
                $pattern
            );
        }

        return $serviceKeys;
    }