docs: public JsonObject toJsonObject(Boolean serializeNulls) {
          Class<? extends BaseCanvasModel> clazz = this.getClass();
          CanvasObject canvasObjectAnnotation = clazz.getAnnotation(CanvasObject.class);
          if(canvasObjectAnnotation == null || canvasObjectAnnotation.postKey() == null) {
              throw new IllegalArgumentException("Object to wrap must have a CanvasObject annotation with a postKey");
          }
          String objectPostKey = canvasObjectAnnotation.postKey();
          JsonElement element = GsonResponseParser.getDefaultGsonParser(serializeNulls).toJsonTree(this);
          JsonObject jsonObject = new JsonObject();
          jsonObject.add(objectPostKey, element);
          return jsonObject;
      }