static boolean empty(int tsBlockIndex, TsBlock[] inputTsBlocks, int[] inputIndex) {
    return inputTsBlocks[tsBlockIndex] == null
        || inputTsBlocks[tsBlockIndex].getPositionCount() == inputIndex[tsBlockIndex];
  }
judge whether TsBlock at tsBlockIndex is empty.

@param tsBlockIndex index
@param inputTsBlocks input TsBlock array
@param inputIndex current index for each input TsBlock and size of it is equal to inputTsBlocks
@return true if TsBlock at tsBlockIndex is null or its current read index is larger than its
    size
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/merge/ColumnMerger.java