Approval where no supervisor for some assignments

Summary:

We are trying to create an approval for withdrawing from a course where the manager is notified of the withdrawal.

The approval works apart from when the person has no supervisor

Content (required):

We are trying to create the approval rule but get where the manager is notified when there is a withdrawal, but when teh person has no supervisor / manager the transaction fails with the error LearningAssignmentWithdrawalApproval rule set failed because a supervisor does not exist for

It is correct that these people do not have supervisors but I have tried to use Lists.resourceListOrManagementChainOrSupervisory. I have tried the GetManager but the function is not allowed for learning and then was going to self approve without a notification.