Expense report approval flow assigning 'null' approver

Summary:

Hello,

Our users recently reported an issue related to an expense report where the system assigned a 'null' approver in the flow. We have the approval flow setup where if an employee submits an expense to a cost center other than their default cost center, it should go to the cost center owner for approval. I can see where the cost center owner is listed as an approver, however it also assigned an approver as 'null'.

I'm attaching a screenshot of the expense report approvals. Has anyone encountered this issue before and found a solution? Any pointers on how I can effectively troubleshoot this?