code: public Observable<ServiceResponse<TopologyInner>> getTopologyWithServiceResponseAsync(String resourceGroupName, String networkWatcherName, TopologyParameters parameters) {
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (networkWatcherName == null) {
              throw new IllegalArgumentException("Parameter networkWatcherName is required and cannot be null.");
          }
          if (this.client.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.client.subscriptionId() is required and cannot be null.");
          }
          if (parameters == null) {
              throw new IllegalArgumentException("Parameter parameters is required and cannot be null.");
          }
          Validator.validate(parameters);
          final String apiVersion = "2018-04-01";
          return service.getTopology(resourceGroupName, networkWatcherName, this.client.subscriptionId(), parameters, apiVersion, this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<TopologyInner>>>() {
                  @Override
                  public Observable<ServiceResponse<TopologyInner>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<TopologyInner> clientResponse = getTopologyDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Gets the current network topology by resource group.
  
  @param resourceGroupName The name of the resource group.
  @param networkWatcherName The name of the network watcher.
  @param parameters Parameters that define the representation of topology.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the TopologyInner object