Fix possible NPE

Description

Fix possible NPE when getting the current token.

Indeed, if authData is empty (which is the default value), fromJson() returns null.

A whole refacto of the way the login work seems mandatory. I added the following issue in the upcoming sprint: https://gitlab.e.foundation/e/os/backlog/-/issues/2784

Screenshots

Technical details

Tests

Issues

https://gitlab.e.foundation/e/os/backlog/-/issues/2963

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