Fix EmailField / URLField required=False

[berycz]

fix for #423

[berycz]

hmm, I'm not sure whether to fix the tests or set default field=None?

[berycz]

maybe rather field=None for backwards compatibility?

[jlubcke]

It would be nice with some test cases showing the different cases.

[boxed]

The existing code has return <something> or string_value but the or can never apply since <something> raises....

[berycz]

yea, I was also thinking what's the point of or string_value :) and I was also thinking if instead of field=None there shouldnt be rather something like allow_empty=False with self.invoke_callback(self.parse, string_value=raw_data, allow_empty=not self.required) on L870?

EDIT: probably not, choice_parse also takes field

[berycz]

oh I got the or string_value validators either raise exception or return "nothing" (None) so if the email/url is valid, then it's return None or string_value

[boxed]

Thanks!