code: public Observable<VpnGatewayInner> createOrUpdateAsync(String resourceGroupName, String gatewayName, VpnGatewayInner vpnGatewayParameters) {
          return createOrUpdateWithServiceResponseAsync(resourceGroupName, gatewayName, vpnGatewayParameters).map(new Func1<ServiceResponse<VpnGatewayInner>, VpnGatewayInner>() {
              @Override
              public VpnGatewayInner call(ServiceResponse<VpnGatewayInner> response) {
                  return response.body();
              }
          });
      }
docs: Creates a virtual wan vpn gateway if it doesn't exist else updates the existing gateway.
  
  @param resourceGroupName The resource group name of the VpnGateway.
  @param gatewayName The name of the gateway.
  @param vpnGatewayParameters Parameters supplied to create or Update a virtual wan vpn gateway.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request