Java Development Tools

Hi ,
I am using jdeveloper version 11.1.1.6.0 .
I am storing session using following code

        abcList  = new ArrayList<abcVO>();             
        JSFUtils.storeOnSession("key",abcList  );

and retrive it using following sentense

         abcList  = (ArrayList<abcVO>) JSFUtils.getFromSession("key");

It is ok I am able to get the session value because I store it first .
But I want to know whether list is stored in session scope earlier if no then want to store it
If data is not present in session and i am getting its value before it is stored it throws null pointer exception

  
        abcList  = (ArrayList<abcVO>) JSFUtils.getFromSession("key");

How to check whether value is null or not null before accessing session.