get_action in EmailMethod raise AttributeError if device has not email value

[EngFarisAlsmawi]

django-two-factor-auth/two_factor/plugins/email/method.py

Line 40 in fe6c940

masked_email = mask_email(device.email)

A method masked_email will be raise AttributeError when invoke get_action method, If you create device instance without email .
AttributeError at /account/two_factor/ 'NoneType' object has no attribute 'split'

This is fields is optional , so that you can used user email field as alternative if device email field is null.

[claudep]

Yes, we should do like https://github.com/django-otp/django-otp/blob/master/src/django_otp/plugins/otp_email/models.py#L70, (device.email or device.user.email). Would you like to provide a patch, with a regression test?