code: public BatchFailureListener<QueryBatch> initializeRetryListener(QueryBatchListener queryBatchListener) {
      if(! retryListenersSet.contains(queryBatchListener)) {
        synchronized(this) {
          if(! retryListenersSet.contains(queryBatchListener)) {
            RetryListener retryListener = new RetryListener(queryBatchListener);
            retryListenersSet.add(queryBatchListener);
            return retryListener;
          }
        }
      }
      return null;
    }
docs: Initializes the RetryListener for the given QueryBatchListener.
  
  @param queryBatchListener the QueryBatchListener for which the RetryListener
  has to be initialized.
  @return the RetryListener if not initialized and null if already initialized.