#vulnerable code 
                                @Override
    public List<Word> seg(String text) {
        List<Word> result = new ArrayList<>();
        List<String> sentences = Punctuation.seg(text, KEEP_PUNCTUATION);
        if(sentences.size() == 1){
            result = segSentence(sentences.get(0));
        }else {
            //如果是多个句子，可以利用多线程提升分词速度
            List<Future<List<Word>>> futures = new ArrayList<>(sentences.size());
            for (String sentence : sentences) {
                futures.add(submit(sentence));
            }
            sentences.clear();
            for (Future<List<Word>> future : futures) {
                List<Word> words;
                try {
                    words = future.get();
                    if (words != null) {
                        result.addAll(words);
                    }
                } catch (InterruptedException | ExecutionException ex) {
                    LOGGER.error("获取分词结果失败", ex);
                }
            }
            futures.clear();
        }
        if(refine) {
            LOGGER.debug("对分词结果进行refine之前：{}", result);
            List<Word> finalResult = refine(result);
            LOGGER.debug("对分词结果进行refine之后：{}", finalResult);
            result.clear();
            return finalResult;
        }else{
            return result;
        }
    } 
                            #location 31 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public List<Word> seg(String text) {
        List<String> sentences = Punctuation.seg(text, KEEP_PUNCTUATION);
        if(sentences.size() == 1){
            return segSentence(sentences.get(0));
        }
        //如果是多个句子，可以利用多线程提升分词速度
        List<Future<List<Word>>> futures = new ArrayList<>(sentences.size());
        for(String sentence : sentences){
            futures.add(submit(sentence));
        }
        sentences.clear();
        List<Word> result = new ArrayList<>();
        for(Future<List<Word>> future : futures){
            List<Word> words;
            try {
                words = future.get();
                if(words != null){
                    result.addAll(words);
                }
            } catch (InterruptedException | ExecutionException ex) {
                LOGGER.error("获取分词结果失败", ex);
            }
        }
        futures.clear();
        return result;
    }