Can't add add_child to Page table?

Question

Django

When adding add_child to Page table

obj_cruise = self.obj_cruise_index.add_child(
                    instance=Cruise(**options))

an error occurs

ОШИБКА:  значение NULL в столбце "translation_key" отношения "wagtailcore_page" нарушает ограничение NOT NULL

But the translation_key should be generated by itself, right? What is the problem here, please?
Thank you in advance!

Answer 1

So instance must be a real object in the database?