@Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    if (!super.equals(o)) {
      return false;
    }
    FillNode that = (FillNode) o;
    return Objects.equals(fillDescriptor, that.fillDescriptor) && scanOrder == that.scanOrder;
  }
FillNode is used to fill the empty field in one row.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/process/FillNode.java