docs: public Observable<ServiceResponse<List<Person>>> listWithServiceResponseAsync(String personGroupId, ListPersonGroupPersonsOptionalParameter listOptionalParameter) {
          if (this.client.azureRegion() == null) {
              throw new IllegalArgumentException("Parameter this.client.azureRegion() is required and cannot be null.");
          }
          if (personGroupId == null) {
              throw new IllegalArgumentException("Parameter personGroupId is required and cannot be null.");
          }
          final String start = listOptionalParameter != null ? listOptionalParameter.start() : null;
          final Integer top = listOptionalParameter != null ? listOptionalParameter.top() : null;
  
          return listWithServiceResponseAsync(personGroupId, start, top);
      }