Adding admin task to manager/buddy who does not exist on new hire will raise error

[GDay]

To reproduce:
Create sequence with an admin task that will be assigned to "manager" or "buddy" (with a comment).
Assign sequence to user without buddy or manager.
This will raise a 500 error. This is due to all admin task comments needing an author and will therefore raise this error:
"null value in column "comment_by_id" of relation "admin_tasks_admintaskcomment" violates not-null constraint"