Common::getUrl

static function getUrl(VolumeFragment $fragment): ?string
{
	$storage = $fragment->getStorage();
	if (!$storage instanceof DiskStorage)
	{
		throw new ArgumentTypeException('Fragment must be subclass of '.DiskStorage::className());
	}

	$url = $storage->getProxyType()->getStorageBaseUrl();

	$testUrl = trim($url, '/');
	if (
		$testUrl == '' ||
		$testUrl == DiskProxyTypeBase::SUFFIX_DISK
	)
	{
		return null;
	}

	return $url;
}