When you create a purchase agreement from the from view of a purchase order , it can have some invalid states which may lead to not having a vendor too. Since choosing a purchase agreement makes the vendor read only on the PO form , then it may lead to having a PO form without a vendor and can't update it. Steps to reproduce the error : 1- activate blanked orders 2- create a new purchase order directly from the PO form opw-3335891 closes odoo/odoo#124528 X-original-commit: 100187e904b85306a7823c54adb78f493abacf78 Signed-off-by: Tiffany Chang <tic@odoo.com> Signed-off-by: Mahdi Cheikh Rouhou (macr) <macr@odoo.com>