code: public Observable<Void> trainAsync(String personGroupId) {
          return trainWithServiceResponseAsync(personGroupId).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Queue a person group training task, the training task may not be started immediately.
  
  @param personGroupId Id referencing a particular person group.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.