.build(), listener);
  }

  static final class SlackJsonAdapters {
    @ToJson String urlToJson(HttpUrl httpUrl) {
      return httpUrl.toString();
    }

    @FromJson HttpUrl urlFromJson(String urlString) {
      if (urlString.startsWith("wss:")) urlString = "https:" + urlString.substring(4);
      if (urlString.startsWith("ws:")) urlString = "http:" + urlString.substring(3);
      return HttpUrl.get(urlString);