code: def _get_or_add_tx_rich(self):
          
          dLbl = self._get_or_add_dLbl()
  
          # having a c:spPr or c:txPr when a c:tx is present causes the "can't
          # save" bug on bubble charts. Remove c:spPr and c:txPr when present.
          dLbl._remove_spPr()
          dLbl._remove_txPr()
  
          return dLbl.get_or_add_tx_rich()
docs: Return the `c:tx` element for this data label, with its `c:rich`
          child and descendants, newly created if not yet present.