Previously, when a user was created through the admin UI, their

extra_data field would be null in the database becuase the field

did not have a value set. This would cause issues when an admin user

created this way would try to access the admin UI, which assumed that

this field was non-null, and an AttributeError exception would be

raised. This patch fixes that issue by ensuring that the user's

extra_data field is non-null at creation time and when accessing

the admin UI.

Ran unit tests.
Verified the following was true:

Admins with extra_data=null are able to access the admin panel.

   Their extra_data field is updated to be an empty dict.
Users created via the admin panel have their extra_data field as

   an empty dict.

These were not true prior to applying the patch