Cannot Instantiate Books properly

[pierre-malis-coopengo]

Cannot Instantiate Books using the book form
This is because exmplary needs to have a unique identifer
This is because the One2Many exemplaries field has a wrong default value
Possible solution:
go from

    @classmethod
    def default_exemplaries(cls):
        return [{}]

to

    @classmethod
    def default_exemplaries(cls):
        return []

https://github.com/coopengo/tryton-training/blob/5.0/step10/modules/library/library.py

this issue is simple to understand but might affect quite a lot of branches
this is especially troubling toward the end of the tutorial since the book form has been stripped from the exemplary page:

https://github.com/coopengo/tryton-training/blob/5.0/step10/modules/library/view/book_form.xml