docs: private synchronized Long getMinTransformedProcessId() {
          if (!CollectionUtils.isEmpty(progress)) {
              Long processId = Collections.min(progress.keySet());
              StageProgress stage = progress.get(processId);
              // stage可能为空，针对select未完成时，对应的值就为null
              if (stage != null && stage != nullProgress && stage.getStage().isTransform()) {
                  return processId;
              }
          }
  
          return null;
      }