Convert this array into a numpy.ma.MaskedArray

        Parameters
        ----------
        copy : bool
            If True (default) make a copy of the array in the result. If False,
            a MaskedArray view of DataArray.values is returned.

        Returns
        -------
        result : MaskedArray
            Masked where invalid values (nan or inf) occur.

def to_masked_array(self, copy=True):
        """Convert this array into a numpy.ma.MaskedArray

        Parameters
        ----------
        copy : bool
            If True (default) make a copy of the array in the result. If False,
            a MaskedArray view of DataArray.values is returned.

        Returns
        -------
        result : MaskedArray
            Masked where invalid values (nan or inf) occur.
        """
        isnull = pd.isnull(self.values)
        return np.ma.MaskedArray(data=self.values, mask=isnull, copy=copy)