To replicate: Create a borrower with no cardnumber (you may have to un-require the cardnumber in your database) Create a patron list Add a borrower with a cardnumber, notice it works Try to add your borrower that has no cardnumber, notice that it doesn't work It looks like we can handle either borrowernumbers or cardnumbers in the back end, but the front end here is sending only half useful ID's.
I have just verified this works now on the current development version.