Return field's value.

        :param DomainModel model:
        :param object default:
        :rtype object:

def get_value(self, model, default=None):
        """Return field's value.

        :param DomainModel model:
        :param object default:
        :rtype object:
        """
        if default is not None:
            default = self._converter(default)

        value = getattr(model, self.storage_name)
        return value if value is not None else default