Error in UserConfigHelper, when accessing cookbook URL, while not being logged in

[awinterstein]

Description
Error in UserConfigHelper, when trying to access the cookbook URL, while not being logged in. A null object instead of a string is given to the constructor in this case.

Reproduction
Steps to reproduce the behavior:

1. Make sure to NOT being logged in at the Nextcloud instance.
2. Open the cookbook URL e.g., http://nextcloud.example.org/index.php/apps/cookbook/#/
3. There's a Nextcloud server error shown
4. In the Nextcloud log file, an error with the following message appears: Argument 1 passed to OCA\Cookbook\Helper\UserConfigHelper::__construct() must be of the type string, null given

Expected behavior
Forward to the Nextcloud login page.

Actual behavior
Nextcloud shows a server error.

Browser
Firefox. The error should be independent of the browser, as it is a backend issue.

Versions
Nextcloud server version: 23.0.3
Cookbook version: 0.9.11
Database system: PostgreSQL