code: public ServiceFuture<Void> trainAsync(String personGroupId, final ServiceCallback<Void> serviceCallback) {
          return ServiceFuture.fromResponse(trainWithServiceResponseAsync(personGroupId), serviceCallback);
      }
docs: Queue a person group training task, the training task may not be started immediately.
  
  @param personGroupId Id referencing a particular person group.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object