How to insert data to database using hibernet & struts

[ghjk]

I want to insert web application data to mysql database. I'm using struts, jsp and hibernet.This is my action class.

public ActionForward execute(ActionMapping mapping, ActionForm form,
            HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        MemberActionForm formbean = (MembeActionForm) form;
       
      
        data.Dvb user = new data.Dvb();
        viewer.setName(formbean.getMembername());
        
        viewer.setBirthDate(formbean.getBirthdate());
       

        Session s = data.DataAccess.getDataAccess().getSession();
        Transaction tr = s.beginTransaction();
        s.save(viewer);
        tr.commit();
        
        return mapping.findForward(SUCCESS);
    }
}

I got the error saying

"org.hibernate. PropertyValueEx ception: not-null property references a null or transient value"

I'm new to struts and hibernet. so still couldn't understand the error.Please help me..