docs: public static HashMap<Integer, List<RebalanceTaskInfo>> groupPartitionsTaskByNode(List<RebalanceTaskInfo> rebalanceTaskPlanList,
                                                                                        boolean groupByStealerNode) {
          HashMap<Integer, List<RebalanceTaskInfo>> nodeToTaskInfo = Maps.newHashMap();
          if(rebalanceTaskPlanList != null) {
              for(RebalanceTaskInfo partitionInfo: rebalanceTaskPlanList) {
                  int nodeId = groupByStealerNode ? partitionInfo.getStealerId()
                                                 : partitionInfo.getDonorId();
                  List<RebalanceTaskInfo> taskInfos = nodeToTaskInfo.get(nodeId);
                  if(taskInfos == null) {
                      taskInfos = Lists.newArrayList();
                      nodeToTaskInfo.put(nodeId, taskInfos);
                  }
                  taskInfos.add(partitionInfo);
              }
          }
          return nodeToTaskInfo;
      }