Request.constructor misses checking for the type of input param

[[e-mail]]

Steps to reproduce:

(1) Open a tab and navigate to any URL;
(2) Run the following code in the Console of Devtools:
```
new Request(undefined)
```
(3) Then this code would be evaluated successfully without throwing any exception.

Actual results:

This code is evaluated successfully without throwing any exception.

Expected results:

As https://fetch.spec.whatwg.org/#requestinfo says, the input param is of RequestInfo type, and RequestInfo is of Request or USVString type. Since the code above sets the input param as undefined, a TypeError exception should be thrown.

[youenn fablet]

I guess it is converted to a USVString.
Chrome and Firefox do have the same behavior.

[youenn fablet]

I do not see a test for it, which might be good to add.
Closing as Invalid since all browsers behave the same.