code: public Observable<ImageIds> getAllImageIdsAsync(String listId) {
          return getAllImageIdsWithServiceResponseAsync(listId).map(new Func1<ServiceResponse<ImageIds>, ImageIds>() {
              @Override
              public ImageIds call(ServiceResponse<ImageIds> response) {
                  return response.body();
              }
          });
      }
docs: Gets all image Ids from the list with list Id equal to list Id passed.
  
  @param listId List Id of the image list.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the ImageIds object