Empty access token considered as a valid

Summary

It happens that an undefined token is used as a valid one.

Steps to reproduce

Not possible to easily reproduce at the moment, but happens after some time (refresh token was in use to fetch the access token).

What is the current bug behavior?

Undefined access token is being sent to the services, as the access token is falsely considered as a valid one.

What is the expected correct behavior?

Should not save the undefined access token in the first place. This state should be recognized by the app's logic.

Possible fixes

Internet connection when refreshing token (getting it from the CAS)?