Currency field in many types has Union type which is so inconvenient

[GLEF1X]

Example from source code

class AmountWithCurrency(Base):
    amount: float
    currency: Union[CurrencyModel, str]  # string if currency util couldn't parse it

For example, like here, user has to introspect currency field and find out whether it str or CurrencyModel. It seems to me that I'll implement this feature with help of python-iso4217 module.