[UPD] Formatting

models/account_invoice.py

@@ -38,6 +38,6 @@ class AccountInvoice(models.Model):
                 "self_id": order.contract_annex_id.id,
                 "active_model": "res.partner.contract.annex",
                 "attachment_model": self._name,
-                "attachment_res_id": self.id
+                "attachment_res_id": self.id,
             },
         }

wizard/res_partner_contract_wizard.py

@@ -226,7 +226,9 @@ class ContractWizard(models.TransientModel, Extension):
 
         self.env["mail.message"].create(
             {
-                "model": self.env.context.get("attachment_model", "res.partner.contract"),
+                "model": self.env.context.get(
+                    "attachment_model", "res.partner.contract"
+                ),
                 "res_id": self.env.context.get("attachment_res_id", res_id),
                 "message_type": "comment",
                 "attachment_ids": [(4, result.id, False)],