def lower(self):
        """Summary

        Returns:
            TYPE: Description
        """
        # TODO : Bug in nested map operating on strings
        # TODO : Check that self.weld_type is a string type
        vectype = self.weld_type
        if isinstance(vectype, WeldVec):
            elem_type = vectype.elemType
            if isinstance(elem_type, WeldChar):
                        return SeriesWeld(
                            grizzly_impl.to_lower(
                                self.expr,
                                elem_type
                            ),
                            self.weld_type,
                            self.df,
                            self.column_name
                        )
        raise Exception("Cannot call to_lower on non string type")