#vulnerable code 
                                @Override
    public Job findByJobClass(Long appId, String clazz) {
        return findById(findIdByJobClass(appId, clazz));
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public Job findByJobClass(Long appId, String clazz) {
        Long jobId = findIdByJobClass(appId, clazz);
        return jobId == null ? null : findById(jobId);
    }