new Request(undefined).url should return "undefined"

[lucacasonato]

See #7836

This is what Chrome, FF, and Safari do, and it is intended behaviour:

• The constructor takes a union type https://fetch.spec.whatwg.org/#requestinfo
• Here's how to process a union type https://heycam.github.io/webidl/#es-union
• Which falls through to step 12
• Which sends us to https://heycam.github.io/webidl/#es-USVString
• Which sends us to https://heycam.github.io/webidl/#es-DOMString
• Which sends us to https://tc39.es/ecma262/#sec-tostring
• Which returns the string "undefined"
• So we process the request constructor with the string input, which takes us to step 6 https://fetch.spec.whatwg.org/#dom-request

[wperron]

for the sake of clarity, both FF and Chrome stringify undefined and interpret it as a relative url when doing new Request(undefined)