docs: public JRBandDataDataSource subDataSource(String bandName) {
          if (containsVisitedBand(bandName))
              return null;
  
          BandData newParentBand = createNewBand(bandName);
  
          currentBand = root;
          currentIterator = root.getChildrenList().iterator();
          visitedBands.put(root, currentIterator);
  
          return new JRBandDataDataSource(newParentBand);
      }