Project owner gets removed when renamed

[christianlupus]

The project owner is cleared once a project is edited.

Steps to reproduce

1. Log in as admin
2. Create a client
3. Create a project for the newly created client
4. See that your admin user is listed as "allowed user" for the project
5. Click on the project and change the title

Expected behavior

The user is still in the list of allowed users

Actual behavior

The list is cleaned.

Additional information

Actually, the backend interprets a non-existing key in the request as an empty list. When tweaking the request and adding the corresponding key in the request, the problem vanishes.