When timer's action tries to end the token it linked to, the scheduler is crashed with Hibernate ObjectNotFound exception due to the token ending removes all timers.

I rewrite SchedulerSession to avoid it(not perfect but workable):

 public void saveTimer(Timer timer) {
 try {
 // if (session.get(timer.getClass(), timer.getId()) != null)
 session.save(timer);
 } catch (ObjectNotFoundException e) {
 log.debug("timer can't be saved; ignore it");
 } catch (Exception e) {
 log.error(e);
 // jbpmSession.handleException();
 throw new JbpmException("couldn't save timer '" + timer
 + "' to the database", e);
 }
 }

 public Iterator findTimersByDueDate() {
 List buffer = new ArrayList();
 CollectionUtils.addAll(buffer, super.findTimersByDueDate());
 return buffer.iterator();
 }