这是我的孔测试代码

Gson gson = new GsonBuilder().setPrettyPrinting().serializeNulls().create();
    JsonWriter jsonWriter = null;
    try {
        jsonWriter = new JsonWriter(
                new OutputStreamWriter(new FileOutputStream(new File("D:/test.json")), "UTF-8"));
        List<String> stringList = new ArrayList<String>();
        stringList.add("aaaaaaaaaaaaaaaaaaaaaa");
        stringList.add("bbbbbbbbbbbbbbbbbbbbbbbb");
        stringList.add("ccccccccccccccccccccccdd");
        Data data = new Data();
        data.setFucName("addXkg");
        data.setSqlList(stringList);
        gson.toJson(data, Data.class, jsonWriter);
        Gson gson1 = new Gson();
        File file = new File("D:/test.json");
        if (file.exists()) {
            JsonReader jsonReader = new JsonReader(new InputStreamReader(new FileInputStream(file), "UTF-8"));

//jsonreader不是null，当涉及到data2时，它在控制面板中显示null

Data data2 = gson1.fromJson(jsonReader, new TypeToken<Data>() {
            }.getType());
            System.out.println(data2);
            for (String string : data2.getSqlList()) {
                System.out.println(string);
            }
        }

它在for（）函数前面返回null，为什么？