code: protected PushMsgBuilder build() {
      ObjectNode result = JsonNodeFactory.instance.objectNode();
      if (criteria != null) {
        result.put("criteria", criteria);
      }
      ObjectNode A = JsonNodeFactory.instance.objectNode();
      ObjectNode msg = JsonNodeFactory.instance.objectNode();
      msg.put("data", data);
      A.put("A", msg);
      result.put("creativeList", A);
      message = result.toString();
      return this;
    }
docs: build message like this:
  {
  "criteria":"{\"deviceToken\":\"APA91bFohTK3UAbjE-8K7R6KuPpmy7tA9fiD41jZFXL2TVzA6zSao2VIuOHfsDDrTB7DfHj7h4piA8w_rStUPvmlYgW4kQmVdgIIG4huZJiQOpgqXEirixz1S_AE18AbI6EMTUF4C2_4\"}",
  "creativeList": {
  "A": {
  "data": {
  "alert":"play poler",
  "aps" : {
  "alert":"play poler"
  }
  }
  }
  }
  }
  
  @return PushMsgBuilder