Establish a `p:bg` child with no-fill settings.

        Any existing `p:bg` child is first removed.

def _change_to_noFill_bg(self):
        """Establish a `p:bg` child with no-fill settings.

        Any existing `p:bg` child is first removed.
        """
        self._remove_bg()
        bg = self.get_or_add_bg()
        bg.add_noFill_bgPr()
        return bg