message: Append Pushdown filter_combiner into the Pullup filter_combiner.
diff: @@ -17,6 +17,8 @@ unique_ptr<LogicalOperator> FilterPushdown::PushdownFilter(unique_ptr<LogicalOpe
  return make_unique<LogicalEmptyResult>(move(op));
  }
  }
  + // append filter combiner to the pullup filter_combiner
  + combiner_pullup.Append(combiner);
  GenerateFilters();
  return Rewrite(move(filter.children[0]));
  }
  