build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  return HtmlWidget(
    htmlString,
    textStyle: textStyle,
    onTapUrl: (String url) async {
      await LaunchUrlHelper.launchURL(url, false);
      return true;
    },
    factoryBuilder: () => SelectableHtmlWidgetFactory(),
    enableCaching: false,
  );
}