The code on 20.11.17 is: # Charge a new rental fee, if applicable my ( $charge, $type ) = GetIssuingCharges( $itemnumber, $borrowernumber ); if ( $charge > 0 ) { AddIssuingCharge($issue, $charge, 'RENT_RENEW'); } But it's the same on current master. The line given is the if-clause in line 3171. The default for rentalcharge and rentalcharge_daily in itemtypes is NULL, maybe that's the cause?