Fixed bug when launching the assignment wizard without udcs on the shipment

This commit refs #27341


(cherry picked from commit dec5c352fe)

shipment.py

@@ -351,7 +351,7 @@ class Assign(metaclass=PoolMeta):
     __name__ = 'stock.shipment.assign'
 
     def transition_start(self):
-        if hasattr(self.record, 'unit_loads'):
+        if getattr(self.record, 'unit_loads', None):
             # if has unit loads, locations may not change
             self.record.assign_force()
             return 'end'