Return values for sorting.

        Returns
        -------
        ndarray
            The transformed values should maintain the ordering between values
            within the array.

        See Also
        --------
        ExtensionArray.argsort

def _values_for_argsort(self) -> np.ndarray:
        """Return values for sorting.

        Returns
        -------
        ndarray
            The transformed values should maintain the ordering between values
            within the array.

        See Also
        --------
        ExtensionArray.argsort
        """
        data = self._data.copy()
        data[self._mask] = data.min() - 1
        return data