code: @Override public void onStageTransition(JobExecutionState state, String previousStage, String newStage) {
      if (_log.isPresent()) {
        _log.get().info("JobExection stage change for " + state.getJobSpec().toShortString() +
                        ": " + previousStage + " --> " + newStage);
      }
    }
docs: {@inheritDoc}