docs: private String getDefaultUserAgent(Request<?> request) {
          String userAgentMarker = request.getOriginalRequest().getRequestClientOptions().getClientMarker(RequestClientOptions
                                                                                                              .Marker.USER_AGENT);
          String userAgent = ClientConfiguration.DEFAULT_USER_AGENT;
          if (StringUtils.hasValue(userAgentMarker)) {
              userAgent += " " + userAgentMarker;
          }
          return userAgent;
      }