Erro 500 Jsf 2.0 + prime faces

]exception 

javax.servlet.ServletException: javax.servlet.ServletException: null source
	br.com.teste.filter.ConexaoHibernateFilter.doFilter(ConexaoHibernateFilter.java:44)


root cause 

javax.servlet.ServletException: null source
	javax.faces.webapp.FacesServlet.service(FacesServlet.java:323)
	br.com.teste.filter.ConexaoHibernateFilter.doFilter(ConexaoHibernateFilter.java:31)


root cause 

java.lang.IllegalArgumentException: null source
	java.util.EventObject.<init>(Unknown Source)
	javax.faces.event.SystemEvent.<init>(SystemEvent.java:67)
	javax.faces.event.ComponentSystemEvent.<init>(ComponentSystemEvent.java:69)
	javax.faces.event.PostRestoreStateEvent.<init>(PostRestoreStateEvent.java:69)
	com.sun.faces.lifecycle.RestoreViewPhase.deliverPostRestoreStateEvent(RestoreViewPhase.java:256)
	com.sun.faces.lifecycle.RestoreViewPhase.execute(RestoreViewPhase.java:245)
	com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
	com.sun.faces.lifecycle.RestoreViewPhase.doPhase(RestoreViewPhase.java:107)
	com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
	javax.faces.webapp.FacesServlet.service(FacesServlet.java:310)
	br.com.teste.filter.ConexaoHibernateFilter.doFilter(ConexaoHibernateFilter.java:31)

public class ConexaoHibernateFilter implements Filter { 


        private SessionFactory sf; 


        @Override 
        public void init(FilterConfig config) throws ServletException { 
                // TODO Auto-generated method stub 
                this.sf = HibernateUtil.getSessionFactory(); 
        } 


        @Override 
        public void doFilter(ServletRequest servletRequest, 
                        ServletResponse servletResponse, FilterChain chain) 
                        throws IOException, ServletException { 
                try { 
                        this.sf.getCurrentSession().beginTransaction(); 
                        chain.doFilter(servletRequest, servletResponse); 
                        this.sf.getCurrentSession().getTransaction().commit(); 
                        this.sf.getCurrentSession().close(); 
                } catch (Throwable ex) { 
                        try { 
                                if (this.sf.getCurrentSession().getTransaction().isActive()) { 
                                        this.sf.getCurrentSession().getTransaction().rollback(); 
                                } 
                        } catch (Throwable t) { 
                                t.printStackTrace(); 
                        } 
                        throw new ServletException(ex); 
                } 
        } 


        @Override 
        public void destroy() { 
                // TODO Auto-generated method stub 


        } 



}