message: rest fix for demo
diff: @@ -388,7 +388,9 @@ int main(int argc, char **argv) {
  string query_ref = random_string(10);
  j["ref"] = query_ref;
  auto chunk = state.res->Fetch();
  + if (chunk != nullptr) {
  serialize_chunk(state.res.get(), chunk.get(), j);
  + }
  {
  std::lock_guard<std::mutex> guard(client_state_map_mutex);
  client_state_map[query_ref] = move(state);
  