title: How is this Quartz Cron Expression executed
body: <p>I have a the following;</p>
  
  <pre><code>private String cronExpression = "";
  private final String jobID = "MyJObID";
  ...
  Scheduler scheduler = ServiceLocator.getInstance().getScheduler();
  CronTrigger trigger = new CronTrigger(jobID , Scheduler.DEFAULT_GROUP, cronExpression);
  JobDetail jobDetail = new JobDetail(jobID , Scheduler.DEFAULT_GROUP, MyJob.class);
  scheduler.scheduleJob(jobDetail, trigger);
  </code></pre>
  
  <p>My question is when is this job triggered for the empty cron expression?</p>