public boolean hasNext() {
    return currentPointElement != null || !pointQueue.isEmpty();
  }
Use those records that share the same timestamp to fill the null sub sensor value in current
TimeValuePair.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/compaction/execute/utils/reader/PointPriorityReader.java