Error while showing notifications

This doesn't work

void _notifyUpdated() async {
  var buttons = new List<chrome.NotificationButton>();
  var individualButton = new chrome.NotificationButton(title: "hello");
  buttons.add(individualButton);
  chrome.NotificationOptions options = new chrome.NotificationOptions();
  options.type = chrome.TemplateType.BASIC;
  options.iconUrl = "/icons/128.png";
  options.title = "Update Notification";
  options.message = "A newer version of abc is installed.";
  options.isClickable = false;
  options.type = chrome.TemplateType.BASIC;
  options.buttons = buttons;
  await chrome.notifications.create(options);
}

This works:

void _notifyUpdated() async {
  //var buttons = new List<chrome.NotificationButton>();
  //var individualButton = new chrome.NotificationButton(title: "hello");
  //buttons.add(individualButton);
  chrome.NotificationOptions options = new chrome.NotificationOptions();
  options.type = chrome.TemplateType.BASIC;
  options.iconUrl = "/icons/128.png";
  options.title = "Update Notification";
  options.message = "A newer version of abc is installed.";
  options.isClickable = false;
  options.type = chrome.TemplateType.BASIC;
  //options.buttons = buttons;
  await chrome.notifications.create(options);
}

I'm trying to hide the default "activate" button by replacing it with other button, what am I doing wrong? or there is a bug ?

Dart sdk: 2.49-dev
chrome.dart version: 0.9.34