@Override
  protected boolean isEmpty(int tsBlockIndex) {
    return inputTsBlocks[tsBlockIndex] == null
        || inputTsBlocks[tsBlockIndex].getPositionCount() == inputIndex[tsBlockIndex];
  }
If the tsBlock of tsBlockIndex is null or has no more data in the tsBlock, return true; else
return false.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/HorizontallyConcatOperator.java