[FIX]account_invoice_fiscal_position_update: fix error when changing …

…fiscal position with a line without product and description

account_invoice_fiscal_position_update/models/account_move.py

@@ -40,5 +40,5 @@ def _onchange_fiscal_position_id_account_invoice_fiscal_position_invoice(self):
                     "to the new Fiscal Position because they don't have a "
                     "Product:\n - %s\nYou should update the Account and the "
                     "Taxes of these invoice lines manually."
-                ) % ("\n- ".join(lines_without_product.mapped("name")))
+                ) % ("\n- ".join([str(k.name) for k in lines_without_product]))
         return res