@Override
  public IQueryDataSource queryForSeriesRegionScan(
      List<IFullPath> pathList,
      QueryContext queryContext,
      Filter globalTimeFilter,
      List<Long> timePartitions)
      throws QueryProcessException {
    return EMPTY_REGION_QUERY_DATA_SOURCE;
  }
It's a virtual data region used for query which contains time series that don't belong to any
data region.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/VirtualDataRegion.java