To whom does the task gets assigned to when an empty role is used as an assignee?
|Knowledge Article Number||000213466|
|Description||When a workflow task has been created and you try to use a role that is empty (users are not assigned to that role), the task gets assigned to the owner of the record where the task is created on.|
This is expected behavior. Similar to how assigning workflow tasks to a role where multiple users are assigned, as referenced on this document: