Features: 1) Initialize order.attributes as an empty dictionary if undefined;

Fixes: 1) Prevent potential errors when accessing `order.attributes` without initialization;

Extra: None;

core/models.py

@@ -1275,6 +1275,9 @@ class PromoCode(ExportModelOperationsMixin("promocode"), NiceModel):  # type: ig
         if self.used_on:
             raise ValueError(_("promocode already used"))
 
+        if not order.attributes:
+            order.attributes = {}
+
         promo_amount = order.total_price
 
         if self.discount_type == "percent":