public function getExpires(): DateTime
    {
        try {
            return $this->headers->get('Expires');
        } catch (\RuntimeException $e) {
            // according to RFC 2616 invalid date formats (e.g. "0" and "-1")
            // must be treated as in the past
            return DateTime::createFromFormat(
                DATE_RFC2822,
                'Sat, 01 Jan 00 00:00:00 +0000'
            );
        }
    }