Es bad url

That `return None` predates the introduction of the ESError class, which is why it's in there, but that's not a good reason to keep it in there.  I think this is a desire to not 500, but in this case, it looks like that's something that *should* 500.  As Danny mentioned, it'd be good to check or for usages of this handling a `None` response, otherwise I think it's correct to raise here.