One can create a repository content selector privilege referencing a content selector id that does not exist.
Example bash script that can do this:
This works even though "test-csel" does not exist.
Now open the screen to edit this privilege in the UI. The "Save" button is enabled and can be clicked to again save the privilege with a null content selector.
1. prevent content selector privileges from being created in the first place with bad references
2. If a priv already does have a reference to a CSEL that no longer exists, the UI should not allow saving the privilege again with a null value.