def start(self, response):
        if not response:
            return Challenge(b"")
        return self.response(response)
Called when the user aborts a click in progress; for example, by
dataset/ETHPy150Open kuri65536/python-for-android/python3-alpha/python-libs/pyxmpp2/sasl/plain.py/PlainServerAuthenticator.start--crossover with--dataset/ETHPy150Open anandology/pyjamas/library/pyjamas/ui/CustomButton.py/CustomButton.onClickCancel