Features: 1) Add validation to return_balance_back to skip execution if status is already "RETURNED"; 2) Raise NotImplementedError when attempting to process a return without an associated user.

Fixes: None;

Extra: None;

engine/core/models.py

@@ -1937,8 +1937,12 @@ class OrderProduct(ExportModelOperationsMixin("order_product"), NiceModel):
         ]
 
     def return_balance_back(self):
+        if self.status == "RETURNED":
+            return
         self.status = "RETURNED"
         self.save()
+        if not self.order.user:
+            raise NotImplementedError
         self.order.user.payments_balance.amount += self.buy_price
         self.order.user.payments_balance.save()