code: public Observable<ServiceResponse<TopicInner>> updateWithServiceResponseAsync(String resourceGroupName, String topicName) {
          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 (topicName == null) {
              throw new IllegalArgumentException("Parameter topicName is required and cannot be null.");
          }
          if (this.client.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.client.apiVersion() is required and cannot be null.");
          }
          final Map<String, String> tags = null;
          TopicUpdateParameters topicUpdateParameters = new TopicUpdateParameters();
          topicUpdateParameters.withTags(null);
          Observable<Response<ResponseBody>> observable = service.update(this.client.subscriptionId(), resourceGroupName, topicName, this.client.apiVersion(), this.client.acceptLanguage(), topicUpdateParameters, this.client.userAgent());
          return client.getAzureClient().getPutOrPatchResultAsync(observable, new TypeToken<TopicInner>() { }.getType());
      }
docs: Update a topic.
  Asynchronously updates a topic with the specified parameters.
  
  @param resourceGroupName The name of the resource group within the user's subscription.
  @param topicName Name of the topic
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request