code: public Observable<ServiceResponse<List<DomainTopicInner>>> listByDomainWithServiceResponseAsync(String resourceGroupName, String domainName) {
          if (this.client.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.client.subscriptionId() is required and cannot be null.");
          }
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (domainName == null) {
              throw new IllegalArgumentException("Parameter domainName is required and cannot be null.");
          }
          if (this.client.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.client.apiVersion() is required and cannot be null.");
          }
          return service.listByDomain(this.client.subscriptionId(), resourceGroupName, domainName, this.client.apiVersion(), this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<List<DomainTopicInner>>>>() {
                  @Override
                  public Observable<ServiceResponse<List<DomainTopicInner>>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<PageImpl<DomainTopicInner>> result = listByDomainDelegate(response);
                          List<DomainTopicInner> items = null;
                          if (result.body() != null) {
                              items = result.body().items();
                          }
                          ServiceResponse<List<DomainTopicInner>> clientResponse = new ServiceResponse<List<DomainTopicInner>>(items, result.response());
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: List domain topics.
  List all the topics in a domain.
  
  @param resourceGroupName The name of the resource group within the user's subscription.
  @param domainName Domain name.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;DomainTopicInner&gt; object