Java初学者使用以下代码将嵌套对象的JSON数组解析为简化的JSON数组。如果JSON元素属性有一个正确的值或null，它工作正常，但如果属性不存在，它将抛出Null指针异常，请帮助我如何在数据解析方法内部处理这个问题。

import com.google.gson.*;

public class DataParser {

    public static JsonArray parseData(JsonArray data) throws JsonParseException {
    JsonArray dataArray = new JsonArray();
        for (JsonElement dataObj : data) {
            
            JsonObject obj = dataObj.getAsJsonObject();
            JsonObject finalDataObj = new JsonObject();            
            JsonObject fieldsObj = obj.getAsJsonObject("fields");
            finalDataObj.add("key", obj.get("key"));
            finalIssueObj.addProperty("cityName", getValue(fieldsObj.get("cityName")));
            finalIssueObj.addProperty("category", getValue(fieldsObj.get("category")));

            dataArray.add(finalDataObj);
        }

        return dataArray;
    }
    
     public static String getValue(JsonElement fieldValue){
         if(fieldValue.isJsonNull()) {
            return "";
        }
        else{
            return fieldValue.getAsString();
        }
    }

}
输入：

[{"key":"1232", "fields": {cityName":"Hyderabad","updated":"2023-05-31","category":"Dining"}},
{"key":"1233", "fields": {cityName":null,"updated":"2023-05-31","category":null}},
{"key":"1234", "fields": {cityName":"Delhi","updated":"2023-04-31"}}]

输出：

[{"key" : "1232", "cityName": "Hyderabad", "category" : "Dining"}, 
{"key" : "1233", "cityName": "", "category" : ""},
{"key" : "1234", "cityName": "Delhi", "category" : ""} ]