docs: public Object[] getGroupData(Object[] data) {
  
          if (isSimpleAggregate) {
              if (simpleAggregateData == null) {
                  simpleAggregateData = data;
  
                  return null;
              }
  
              return simpleAggregateData;
          }
  
          RowIterator it = groupIndex.findFirstRow(session, store, data);
  
          if (it.hasNext()) {
              Row row = it.getNextRow();
  
              if (isAggregate) {
                  row.setChanged();
              }
  
              return row.getData();
          }
  
          return null;
      }