@Override
  protected boolean canSkipCurrentChild(int currentChildIndex) {
    return noMoreTsBlocks[currentChildIndex]
        || !isEmpty(currentChildIndex)
        || children.get(currentChildIndex) == null;
  }
@param currentChildIndex the index of the child
@return true if we can skip the currentChild in prepareInput
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/MergeSortOperator.java