protected function getHeaders(string $key, int $limit, int $after = null, array $merge = [])
    {
        $remaining = $after === null ? $this->limiter->retriesLeft($key, $limit) : 0;
        $headers = ['X-RateLimit-Limit' => $limit, 'X-RateLimit-Remaining' => $remaining];

        return array_merge($headers, $merge);
    }