#vulnerable code 
                                public Class toClass()
        throws NotFoundException, IOException, CannotCompileException
    {
        return getClassPool().toClass(this);
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public Class toClass()
        throws CannotCompileException
    {
        return toClass(Thread.currentThread().getContextClassLoader());
    }