With the ability to tick a checkbox "this edition does not have an author" we made the author credits optional, but the work was not fully finished and there are some display issues.

Refer to this forum post for more details, but in short:
All of the issues below happen for Editions and Edition Groups both, suposedly.

1. creating an edition with no AC works, but when you load that edition page the warning about unset AC is show, which should not be the case
2. when editing that edition, the AC editor is shown with the "no author" checkbox not ticked
3. after ticking it, the AC editor gets greyed out, but the checkbox is still unchecked
4. At that stage, clicking the submit button results in a submission error and crashed the server