code: public Observable<ServiceResponse<List<PersonGroup>>> listWithServiceResponseAsync(ListPersonGroupsOptionalParameter listOptionalParameter) {
          if (this.client.azureRegion() == null) {
              throw new IllegalArgumentException("Parameter this.client.azureRegion() is required and cannot be null.");
          }
          final String start = listOptionalParameter != null ? listOptionalParameter.start() : null;
          final Integer top = listOptionalParameter != null ? listOptionalParameter.top() : null;
  
          return listWithServiceResponseAsync(start, top);
      }
docs: List person groups and their information.
  
  @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;PersonGroup&gt; object