WO will be released and should not go for approval if Project Number is null

Summary:

I have enabled Capex Project detail in Work Order page. The Project Number will be added at the time of Work Order creation. When I am going to release the Work Order it will for respective Project Manager approval. 

BPM Rule: WorkOrderDeferredApprovalPayloadType.pjcProjectNumber isn't null

If I will not add project information when creating any Work order, it should be released directly if I want to release the same. It should not go for Project Manager approval as Project information is not available in this Work order. But it is going for Capex Project Manager approval.

Please suggest what should be the BPM rule or any other way to restrict this