private function formatPort($port = null): ?int
    {
        if (null === $port || '' === $port) {
            return null;
        }

        if (!is_int($port) && !(is_string($port) && 1 === preg_match('/^\d*$/', $port))) {
            throw new SyntaxError(sprintf('The port `%s` is invalid', $port));
        }

        $port = (int) $port;
        if (0 > $port) {
            throw new SyntaxError(sprintf('The port `%s` is invalid', $port));
        }

        $defaultPort = self::SCHEME_DEFAULT_PORT[$this->scheme] ?? null;
        if ($defaultPort === $port) {
            return null;
        }

        return $port;
    }