This code is partially duplicating `JsonCallback.onSuccess` and has similar issues (e.g. not using `JSONObject.NULL`).

I'd like to see a simpler implementation, e.g.

```java
public abstract static class JsonObjectCallback implements JsonCallback {
    @Override
    public final void onSuccess(JSONArray response) throws JSONException {
       onError(new JSONException("Expecting a JSON object: " + response));
    }
}