Android - Error java.lang.UnsupportedOperationException: JsonNull

Question

I am trying to use JSON string, Retrofit and other things in my application. But in this particular model something is making my JSON string to be null.

This is the method where I deserialize my string:

public static class TaskGSON implements JsonSerializer<Task>, JsonDeserializer<Task>{

    @Override
    public Task deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
      System.out.println(json.toString());
      if (!json.isJsonNull()) {
        final JsonObject jsonObject = json.getAsJsonObject();
        Task t = new Task();
        t.mId = jsonObject.get(NAMES.Server.ID).getAsString();
        t.mProjectId = jsonObject.get(NAMES.Server.PROJECT_ID).getAsString();
        t.mTitle = jsonObject.get(NAMES.Server.TITLE).getAsString();
        t.mPriority = Priority.deSerialize(jsonObject.get(NAMES.Server.PRIORITY).getAsString());
        t.mCreatedAt = context.deserialize(jsonObject.get(NAMES.Server.CREATED_AT), Date.class);
        t.mCreatedById = jsonObject.get(NAMES.Server.CREATED_BY_ID).getAsString();
        t.mUpdatedAt = context.deserialize(jsonObject.get(NAMES.Server.UPDATED_AT), Date.class);
        t.mFeedCount = jsonObject.get(NAMES.Server.FEED_COUNT).getAsInt();
        t.mPermissions = context.deserialize(jsonObject.get(NAMES.Server.PERMISSIONS), new TypeToken<List<Permission>>() {}.getType());

        if (jsonObject.has(NAMES.Server.COLLECTION_ID)) {
          t.mCollectionId = jsonObject.get(NAMES.Server.COLLECTION_ID).getAsString();
        }

        if (jsonObject.has(NAMES.Server.DESCRIPTION)) {
          t.mDescription = jsonObject.get(NAMES.Server.DESCRIPTION).getAsString();
        }
        if (jsonObject.has(NAMES.Server.DUE_DATE) && !jsonObject.get(NAMES.Server.DUE_DATE).isJsonNull()) {
          t.mDueDate = context.deserialize(jsonObject.get(NAMES.Server.DUE_DATE), Date.class);
        }

        if (jsonObject.has(NAMES.Server.COMPLETED_AT)) {
          t.mCompletedAt = context.deserialize(jsonObject.get(NAMES.Server.COMPLETED_AT), Date.class);
        }

        if (jsonObject.has(NAMES.Server.COMPLETED_BY_ID)) {
          t.mCompletedById = jsonObject.get(NAMES.Server.COMPLETED_BY_ID).getAsString();
        }

        if (jsonObject.has(NAMES.Server.DELETED_AT)) {
          t.mDeletedAt = context.deserialize(jsonObject.get(NAMES.Server.DELETED_AT), Date.class);
        }

        if (jsonObject.has(NAMES.Server.COMPLETED)) {
          t.mCompleted = jsonObject.get(NAMES.Server.COMPLETED).getAsBoolean();
        }

        if (jsonObject.has(NAMES.Server.CHECKLIST)) {
          t.mChecklists = context.deserialize(jsonObject.get(NAMES.Server.CHECKLIST), new TypeToken<List<Checklist>>() {}.getType());
        }

        if (jsonObject.has(NAMES.Server.ATTACHMENTS)) {
          t.mAttachments = context.deserialize(jsonObject.get(NAMES.Server.ATTACHMENTS), new TypeToken<List<Attachment>>() {}.getType());
        }

        if (jsonObject.has(NAMES.Server.MARKERS)) {
          t.mMarkers = context.deserialize(jsonObject.get(NAMES.Server.MARKERS), new TypeToken<List<Marker>>() {}.getType());
        }
        if (jsonObject.has(NAMES.Server.CATEGORY_ID)) {
         t.mCategory = jsonObject.get(NAMES.Server.CATEGORY_ID).getAsString();
        }

        return t;
      } else {
        return null;
      }
    }

So, the problem is that, when I comment the lines of code that check if there's a field "description" and "categoryId" in my JSON string I don't get the error, but if I uncomment these if statements I get the error saying that the Json is null. And I don't know why.

This is the complete logcat:

09-22 17:02:57.890 21172-26613/com.construct.test E/AbstractEntitiesViewModel: Error java.lang.UnsupportedOperationException: JsonNull
   at com.google.gson.JsonElement.getAsString(JsonElement.java:191)
   at com.construct.v2.models.entities.task.Task$TaskGSON.deserialize(Task.java:740)
   at com.construct.v2.models.entities.task.Task$TaskGSON.deserialize(Task.java:717)
   at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
   at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
   at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
   at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
   at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:37)
   at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:25)
   at retrofit2.ServiceMethod.toResponse(ServiceMethod.java:119)
   at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:218)
   at retrofit2.OkHttpCall.execute(OkHttpCall.java:180)
   at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:40)
   at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:24)
   at retrofit2.adapter.rxjava.BodyOnSubscribe.call(BodyOnSubscribe.java:36)
   at retrofit2.adapter.rxjava.BodyOnSubscribe.call(BodyOnSubscribe.java:28)
   at rx.Observable.unsafeSubscribe(Observable.java:10256)
   at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48)
   at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
   at rx.Observable.unsafeSubscribe(Observable.java:10256)
   at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:248)
   at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:148)
   at rx.internal.operators.OnSubscribeFromArray$FromArrayProducer.fastPath(OnSubscribeFromArray.java:76)
   at rx.internal.operators.OnSubscribeFromArray$FromArrayProducer.request(OnSubscribeFromArray.java:58)
   at rx.Subscriber.setProducer(Subscriber.java:211)
   at rx.internal.operators.OnSubscribeFromArray.call(OnSubscribeFromArray.java:32)
   at rx.internal.operators.OnSubscribeFromArray.call(OnSubscribeFromArray.java:24)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
   at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
   at rx.Observable.unsafeSubscribe(Observable.java:10256)
   at rx.internal.operators.OperatorSubscribeOn$SubscribeOnSubscriber.call(OperatorSubscribeOn.java:100)
   at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:428)
   at java.util.concurrent.FutureTask.run(FutureTask.java:237)
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
   at java.lang.Thread.run(Thread.java:761)

Both fields description and category can be null, but they exist in my Json. It's weird because it works just fine when I comment the lines.

Answer 1

You should change from yourJsonObject.getAsString() to yourJsonObject.toString()