Have campaigns with no authors

[manonviallet]

Description

Once an author has been added to a campaign, it can be changed but not suppressed.

Reproducible Steps

Steps to create the smallest reproducible scenario:

1. Go to the campaign menu
2. Create a new campaign with an author and close the window
3. Try to empty the author field

Expected Output

it should be possible for the author field to be emptied.

Actual Output

The author field can be empty if no author is added when it is created, but if an author is added, then the author field cannot be empty anymore.