Null Condition on Transfer Workflow

Summary:

We are facing issues whilst adding null condition on transfer workflow

Content (please ensure you mask any confidential information):

Hello,

We have transfer approval rule by roles (i.e. we have multiple nodes- one for each role. See screenshot below). I want to add null condition to the approval rule but it is giving me this error. Can someone please let me know as to why is this happening and what can be done to resolve this.

Error:

The current approval rule (for one of those nodes):

((GetManager("LINE_MANAGER",Task.payload.Worker's Current Assignment.result.Assignment Supervisor) == transactionApprovalRequest.Requestor) AND (Worker's Current Assignment.result.Worker Category == "WDR_RES") AND (Worker's Salary Details.Proposed Change Percent >= 20) AND (NOT (GetAllRepresentatives("WDR_HR_DM",Task.payload.Worker's Current Representative.result) contains GetManager("LINE_MANAGER",Task.payload.Worker's Current Assignment.result.Assignment Supervisor))) AND (NOT (GetAllRepresentatives("HR_REP",Task.payload.Worker's Current Representative.result) contains GetManager("LINE_MANAGER",Task.payload.Worker's Current Assignment.result.Assignment Supervisor))))