Get a list of the underlying ``Money`` instances that are not zero

        Returns:
            ([Money]): A list of zero or more money instances. Currencies will be unique.

def nonzero_monies(self):
        """Get a list of the underlying ``Money`` instances that are not zero

        Returns:
            ([Money]): A list of zero or more money instances. Currencies will be unique.
        """
        return [copy.copy(m) for m in self._money_obs if m.amount != 0]