code: public void addInternalJobListener (final IJobListener jobListener)
    {
      ValueEnforcer.notNull (jobListener, "JobListener");
      ValueEnforcer.notEmpty (jobListener.getName (), "JobListener.getName()");
  
      synchronized (m_aInternalJobListeners)
      {
        m_aInternalJobListeners.put (jobListener.getName (), jobListener);
      }
    }
docs: <p>
  Add the given <code>{@link com.helger.quartz.IJobListener}</code> to the
  <code>Scheduler</code>'s <i>internal</i> list.
  </p>