code: public Observable<List<Person>> listAsync(String personGroupId, ListPersonGroupPersonsOptionalParameter listOptionalParameter) {
          return listWithServiceResponseAsync(personGroupId, listOptionalParameter).map(new Func1<ServiceResponse<List<Person>>, List<Person>>() {
              @Override
              public List<Person> call(ServiceResponse<List<Person>> response) {
                  return response.body();
              }
          });
      }
docs: List all persons in a person group, and retrieve person information (including personId, name, userData and persistedFaceIds of registered faces of the person).
  
  @param personGroupId Id referencing a particular person group.
  @param listOptionalParameter 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 List&lt;Person&gt; object