    name: str
    # Fields used in dependencies MUST be declared with `field`
    credit_card: NotNull[int] = field(default=None)
    billing_address: NotNull[str] = field(default=None)

    dependencies = dependent_required({credit_card: [billing_address]})


# it can also be done outside the class with
# dependent_required({"credit_card": ["billing_address"]}, owner=Billing)
