Validation for Empty Objects on Object Level

[julian-r]

ATM the validation of empty object is only working in dict form.

Example:

 RootModel(
        field_a="a", list_items=[ListItem(), ListItem(), ListItem()]
    ).dict() == {"field_a": "a"}

does not raise an validation error. But it actually should.

RootModel(**{"field_a": "a", "list_items": [{}, {}, {}]})

Does.

The problem is in resource header strip_empty_items since it only takes care about the dict representation of the model, which is not executed in case of the construction via Objects. A similar functionality needs to be implemented on a Pydantic object level without the pre parameter in the validator. This should then cover the json variant as well.

[julian-r]

the tests should be renamed as well. Thanks @trojanowski