[Koha] Vendor invoice - required field?

When receiving a shipment in Koha Acquisitions, is the Vendor invoice a required field in Koha now? We have an older version of Koha and are upgrading. We are finding that we need to enter a Vendor Invoice number now which was not required in the earlier version. In general, invoice number makes little sense when paying with credit cards anyway. Is there any workaround for this? Thanks Tom Hanstra