code: public Observable<Image> addImageAsync(String listId, AddImageOptionalParameter addImageOptionalParameter) {
          return addImageWithServiceResponseAsync(listId, addImageOptionalParameter).map(new Func1<ServiceResponse<Image>, Image>() {
              @Override
              public Image call(ServiceResponse<Image> response) {
                  return response.body();
              }
          });
      }
docs: Add an image to the list with list Id equal to list Id passed.
  
  @param listId List Id of the image list.
  @param addImageOptionalParameter 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 Image object