Need to Setup separate approval for PO matched and Non PO matched Invoices in BPM?

Summary:

Need to Setup separate approval for PO matched and Non PO matched Invoices in BPM not through spreadsheet approvals?

Below are the current conditions, however we identified that the Invoice Header.PO Number condition is not working as expected.

PO Matched Rule
Invoice Header.Business Unit Name is "Paradise Island Resort"
and
Invoice Header.PO Number isn't null

NON PO Matched Rule
Invoice Header.Business Unit Name is "Paradise Island Resort"

and

Invoice Header.PO Number is null

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