While the `url` parameter is optional for `$httpBackend.when`,
`$httpBackend.expect` and related shortcut methods, it should not have the
value of `undefined` if it has been provided.
This change ensures that an error is thrown in those cases.
Closes#8442Closes#8462Closes#10934Closes#12777
BREAKING CHANGE
It is no longer valid to explicitly pass `undefined` as the `url` argument
to any of the `$httpBackend.when...()` and `$httpBackend.expect...()`
methods.
While this argument is optional, it must have a defined value if it is
provided.
Previously passing an explicit `undefined` value was ignored but this
lead to invalid tests passing unexpectedly.
Peter Bacon Darwin
7551b8975a