Make Purchase Order promised date required

Summary:

There is a requirement during PO creation to make the PO line promised date required so the buyer will not be able to forget to populate the field.

I was able to do this using sandbox, however, it only works if the buyer will run through all the PO lines. If in case the buyer will not run through the PO line and the Promised date is blank, there is no warning or error message, thus allowing the PO to be submitted with incomplete information required.

Is there a way the system can validate that a PO line is missing this information?