code: public Observable<PersonGroup> getAsync(String personGroupId) {
          return getWithServiceResponseAsync(personGroupId).map(new Func1<ServiceResponse<PersonGroup>, PersonGroup>() {
              @Override
              public PersonGroup call(ServiceResponse<PersonGroup> response) {
                  return response.body();
              }
          });
      }
docs: Retrieve the information of a person group, including its name and userData.
  
  @param personGroupId Id referencing a particular person group.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PersonGroup object