code: def get_dLbl(self, idx):
          
          dLbls = self.dLbls
          if dLbls is None:
              return None
          return dLbls.get_dLbl_for_point(idx)
docs: Return the `c:dLbl` element representing the label for the data point
          at offset *idx* in this series, or |None| if not present.