code: public Observable<TopicInner> beginUpdateAsync(String resourceGroupName, String topicName, Map<String, String> tags) {
          return beginUpdateWithServiceResponseAsync(resourceGroupName, topicName, tags).map(new Func1<ServiceResponse<TopicInner>, TopicInner>() {
              @Override
              public TopicInner call(ServiceResponse<TopicInner> response) {
                  return response.body();
              }
          });
      }
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
  @param tags Tags of the resource
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the TopicInner object