hibernate session.save报空指针，求指教,该如何解决

hibernate session.save报空指针，，求指教

Java code

public void saveStudent(Student student){        try {            transaction = (org.hibernate.Transaction)session.beginTransaction();            session.save(student);            transaction.commit();        } catch (Exception e) {                transaction.rollback();        }finally{            session.close();        }            }