Spring + hibernate org.hibernate.AssertionFailure after insert fails in database

[ashish kulkarni]

I am using spring 3.0 and hibernate 3.0, i am using spring to manage hibernate transaction, when ever i have error when inserting or updating data in database i get following exception

The code in controller is as below, so i am catching saveAirport method, so i am expecting the page getting redirected to reference/add_airport.jsp, but it throws error, any ideas how to handle this issue

 @RequestMapping(value = "/addAirport")
    public String addAirport(@RequestParam("type") String type, @ModelAttribute("newairport") Airport newairport, BindingResult result, Model model, HttpServletRequest request)throws Exception{
   try{
airportDao.saveAirport(newairport);
}
catch(Exception exc){
result.addError(new ObjectError("Error",exc.getMessage() )); 
return "reference/add_airport"; 
}
  }

org.hibernate.AssertionFailure: null id in com.tauck.model.Airport entry (don't flush the Session after an exception occurs)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:82)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:190)
	at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:147)
	at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)
	at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
	at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
	at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)
	at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:383)
	at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:133)
	at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:656)