code: public Observable<ServiceResponse<String>> generatevpnclientpackageWithServiceResponseAsync(String resourceGroupName, String virtualNetworkGatewayName, VpnClientParameters parameters) {
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (virtualNetworkGatewayName == null) {
              throw new IllegalArgumentException("Parameter virtualNetworkGatewayName 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 = "2018-06-01";
          Observable<Response<ResponseBody>> observable = service.generatevpnclientpackage(resourceGroupName, virtualNetworkGatewayName, this.client.subscriptionId(), parameters, apiVersion, this.client.acceptLanguage(), this.client.userAgent());
          return client.getAzureClient().getPostOrDeleteResultAsync(observable, new TypeToken<String>() { }.getType());
      }
docs: Generates VPN client package for P2S client of the virtual network gateway in the specified resource group.
  
  @param resourceGroupName The name of the resource group.
  @param virtualNetworkGatewayName The name of the virtual network gateway.
  @param parameters Parameters supplied to the generate virtual network gateway VPN client package operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request