Override ndarray.argsort. Argsorts the value, omitting NA/null values,
        and places the result in the same locations as the non-NA values.

        Parameters
        ----------
        axis : int
            Has no effect but is accepted for compatibility with numpy.
        kind : {'mergesort', 'quicksort', 'heapsort'}, default 'quicksort'
            Choice of sorting algorithm. See np.sort for more
            information. 'mergesort' is the only stable algorithm
        order : None
            Has no effect but is accepted for compatibility with numpy.

        Returns
        -------
        Series
            Positions of values within the sort order with -1 indicating
            nan values.

        See Also
        --------
        numpy.ndarray.argsort

def argsort(self, axis=0, kind='quicksort', order=None):
        """
        Override ndarray.argsort. Argsorts the value, omitting NA/null values,
        and places the result in the same locations as the non-NA values.

        Parameters
        ----------
        axis : int
            Has no effect but is accepted for compatibility with numpy.
        kind : {'mergesort', 'quicksort', 'heapsort'}, default 'quicksort'
            Choice of sorting algorithm. See np.sort for more
            information. 'mergesort' is the only stable algorithm
        order : None
            Has no effect but is accepted for compatibility with numpy.

        Returns
        -------
        Series
            Positions of values within the sort order with -1 indicating
            nan values.

        See Also
        --------
        numpy.ndarray.argsort
        """
        values = self._values
        mask = isna(values)

        if mask.any():
            result = Series(-1, index=self.index, name=self.name,
                            dtype='int64')
            notmask = ~mask
            result[notmask] = np.argsort(values[notmask], kind=kind)
            return self._constructor(result,
                                     index=self.index).__finalize__(self)
        else:
            return self._constructor(
                np.argsort(values, kind=kind), index=self.index,
                dtype='int64').__finalize__(self)