code: public final NotificationChannel updateNotificationChannel(
        FieldMask updateMask, NotificationChannel notificationChannel) {
  
      UpdateNotificationChannelRequest request =
          UpdateNotificationChannelRequest.newBuilder()
              .setUpdateMask(updateMask)
              .setNotificationChannel(notificationChannel)
              .build();
      return updateNotificationChannel(request);
    }
docs: Updates a notification channel. Fields not specified in the field mask remain unchanged.
  
  <p>Sample code:
  
  <pre><code>
  try (NotificationChannelServiceClient notificationChannelServiceClient = NotificationChannelServiceClient.create()) {
  FieldMask updateMask = FieldMask.newBuilder().build();
  NotificationChannel notificationChannel = NotificationChannel.newBuilder().build();
  NotificationChannel response = notificationChannelServiceClient.updateNotificationChannel(updateMask, notificationChannel);
  }
  </code></pre>
  
  @param updateMask The fields to update.
  @param notificationChannel A description of the changes to be applied to the specified
  notification channel. The description must provide a definition for fields to be updated;
  the names of these fields should also be included in the `update_mask`.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails