code: public Observable<List<DetectedFace>> detectWithUrlAsync(String url, DetectWithUrlOptionalParameter detectWithUrlOptionalParameter) {
          return detectWithUrlWithServiceResponseAsync(url, detectWithUrlOptionalParameter).map(new Func1<ServiceResponse<List<DetectedFace>>, List<DetectedFace>>() {
              @Override
              public List<DetectedFace> call(ServiceResponse<List<DetectedFace>> response) {
                  return response.body();
              }
          });
      }
docs: Detect human faces in an image and returns face locations, and optionally with faceIds, landmarks, and attributes.
  
  @param url Publicly reachable URL of an image
  @param detectWithUrlOptionalParameter the object representing the optional parameters to be set before calling this API
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;DetectedFace&gt; object