code: public Observable<ServiceResponse<VirtualWANInner>> createOrUpdateWithServiceResponseAsync(String resourceGroupName, String virtualWANName, VirtualWANInner wANParameters) {
          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 (virtualWANName == null) {
              throw new IllegalArgumentException("Parameter virtualWANName is required and cannot be null.");
          }
          if (wANParameters == null) {
              throw new IllegalArgumentException("Parameter wANParameters is required and cannot be null.");
          }
          Validator.validate(wANParameters);
          final String apiVersion = "2018-04-01";
          Observable<Response<ResponseBody>> observable = service.createOrUpdate(this.client.subscriptionId(), resourceGroupName, virtualWANName, apiVersion, wANParameters, this.client.acceptLanguage(), this.client.userAgent());
          return client.getAzureClient().getPutOrPatchResultAsync(observable, new TypeToken<VirtualWANInner>() { }.getType());
      }
docs: Creates a VirtualWAN resource if it doesn't exist else updates the existing VirtualWAN.
  
  @param resourceGroupName The resource group name of the VirtualWan.
  @param virtualWANName The name of the VirtualWAN being created or updated.
  @param wANParameters Parameters supplied to create or update VirtualWAN.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request