[FIX] partner without city_id

base_location/models/res_partner.py

@@ -83,7 +83,7 @@ class ResPartner(models.Model):
                 raise ValidationError(_(
                     "The country of the partner %s differs from that in "
                     "location %s") % (rec.name, rec.zip_id.name))
-            if rec.zip_id.city_id != rec.city_id:
+            if rec.city_id and rec.zip_id.city_id != rec.city_id:
                 raise ValidationError(_(
                     "The city of partner %s differs from that in "
                     "location %s") % (rec.name, rec.zip_id.name))