code: private void addInternalJobListener(JobListener jobListener) {
  
      if (jobListener.getName() == null || jobListener.getName().length() == 0) {
        throw new IllegalArgumentException("JobListener name cannot be empty.");
      }
  
      synchronized (internalJobListeners) {
        internalJobListeners.put(jobListener.getName(), jobListener);
      }
    }
docs: Add the given <code>{@link org.quartz.listeners.JobListener}</code> to the <code>Scheduler
  </code>'s <i>internal</i> list.