cloud.users api throwing assert error on local development

When trying to use users.get_current_user(), this line gives an assertion error which prevents the app from running locally:
https://github.com/google/gae-secure-scaffold-python3/blob/master/src/securescaffold/contrib/appengine/users.py#L69

As a current solution we wrap it in a try/catch, using a default email on an exception.

Is possible to have a mock user for a local environment, or similar?