Homebrew recipe without url
You have to use an url in your receipt, that's mandatory.

You don't have to use the http(s) url scheme, you can also use file:. If you don't need any content, you can use the /dev/null file. It can even have a checksum to silence the related warning.

url "file:///dev/null"
sha256 "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"