@Override
  protected void serializeAttributes(DataOutputStream stream) throws IOException {
    PlanNodeType.FILTER.serialize(stream);
    ReadWriteIOUtils.write(outputExpressions.length, stream);
    for (Expression expression : outputExpressions) {
      Expression.serialize(expression, stream);
    }
    Expression.serialize(predicate, stream);
    ReadWriteIOUtils.write(keepNull, stream);
    ReadWriteIOUtils.write(scanOrder.ordinal(), stream);
  }
This construction method is only used in inner of class `FilterNode`.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/process/FilterNode.java