code: public Observable<ServiceResponse<ExpressRouteConnectionInner>> createOrUpdateWithServiceResponseAsync(String resourceGroupName, String expressRouteGatewayName, String connectionName, ExpressRouteConnectionInner putExpressRouteConnectionParameters) {
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (expressRouteGatewayName == null) {
              throw new IllegalArgumentException("Parameter expressRouteGatewayName is required and cannot be null.");
          }
          if (connectionName == null) {
              throw new IllegalArgumentException("Parameter connectionName 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 (putExpressRouteConnectionParameters == null) {
              throw new IllegalArgumentException("Parameter putExpressRouteConnectionParameters is required and cannot be null.");
          }
          Validator.validate(putExpressRouteConnectionParameters);
          final String apiVersion = "2018-08-01";
          Observable<Response<ResponseBody>> observable = service.createOrUpdate(resourceGroupName, expressRouteGatewayName, connectionName, this.client.subscriptionId(), putExpressRouteConnectionParameters, apiVersion, this.client.acceptLanguage(), this.client.userAgent());
          return client.getAzureClient().getPutOrPatchResultAsync(observable, new TypeToken<ExpressRouteConnectionInner>() { }.getType());
      }
docs: Creates a connection between an ExpressRoute gateway and an ExpressRoute circuit.
  
  @param resourceGroupName The name of the resource group.
  @param expressRouteGatewayName The name of the ExpressRoute gateway.
  @param connectionName The name of the connection subresource.
  @param putExpressRouteConnectionParameters Parameters required in an ExpressRouteConnection PUT operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request