message: added nullptr checking
diff: @@ -7,6 +7,8 @@ QueryWorker::QueryWorker(const std::string &configFile, adios2::Engine &reader)
  {
  adios2::query::Worker *m =
  adios2::query::GetWorker(configFile, reader.m_Engine);
  + if (m == nullptr)
  + throw std::invalid_argument("ERROR: unable to construct query. ");
  m_Worker = std::make_shared<adios2::query::Worker>(*m);
  }
  @@ -14,6 +16,7 @@ void QueryWorker::GetResultCoverage(
  adios2::Box<adios2::Dims> &outputSelection,
  std::vector<adios2::Box<adios2::Dims>> &touched_blocks)
  {
  + if (m_Worker)
  return m_Worker->GetResultCoverage(outputSelection, touched_blocks);
  }
  }
  