message: properly set has_null in HT when merging
diff: @@ -79,13 +79,15 @@ void JoinHashTable::Merge(JoinHashTable &other) {
  swizzled_string_heap->Merge(*other.swizzled_string_heap);
  }
  - // TODO: merge correlated mark join info
  - if (join_type == JoinType::MARK && !correlated_mark_join_info.correlated_types.empty()) {
  + if (join_type == JoinType::MARK) {
  auto &info = correlated_mark_join_info;
  - auto &other_info = other.correlated_mark_join_info;
  lock_guard<mutex> mj_lock(info.mj_lock);
  + has_null = has_null || other.has_null;
  + if (!correlated_mark_join_info.correlated_types.empty()) {
  + auto &other_info = other.correlated_mark_join_info;
  info.correlated_counts->Combine(*other_info.correlated_counts);
  }
  + }
  lock_guard<mutex> lock(partition_lock);
  if (partition_block_collections.empty()) {
  