[FIX] creation of invoice

models/sale.py

@@ -53,7 +53,9 @@ class SaleOrder(models.Model):
         values = super()._prepare_invoice()
         values.update(
             {
-                "user_second_ids": fields.Command.create(self.user_second_ids.ids),
+                "user_second_ids": fields.Command.create(self.user_second_ids.ids)
+                if self.user_second_ids
+                else False,
                 "user_provider_id": self.user_provider_id.id or False,
             }
         )