code: public Observable<Void> updateAsync(String personGroupId, UpdatePersonGroupsOptionalParameter updateOptionalParameter) {
          return updateWithServiceResponseAsync(personGroupId, updateOptionalParameter).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Update an existing person group's display name and userData. The properties which does not appear in request body will not be updated.
  
  @param personGroupId Id referencing a particular person group.
  @param updateOptionalParameter the object representing the optional parameters to be set before calling this API
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.