Use compat function in place of call to user.is_authenticated()
@@ -198,7 +198,7 @@ class OrderPlacementMixin(CheckoutSessionMixin):
if not billing_address:
return None
billing_address.save()
- if user.is_authenticated():
+ if user_is_authenticated(user):
self.update_address_book(user, billing_address)
return billing_address
