code: public Observable<FaceList> getAsync(String faceListId) {
          return getWithServiceResponseAsync(faceListId).map(new Func1<ServiceResponse<FaceList>, FaceList>() {
              @Override
              public FaceList call(ServiceResponse<FaceList> response) {
                  return response.body();
              }
          });
      }
docs: Retrieve a face list's information.
  
  @param faceListId Id referencing a particular face list.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the FaceList object