Fixing `Caught error: Unsupported operation: Platform._operatingSystem`

I recently added Web support to an existing mobile Flutter app and got this error when running it in Chrome:

Caught error: Unsupported operation: Platform._operatingSystem

It turns out it is a known issue in Flutter Web, from July 2019: If you use platform.isAndroid or platform.isIOS, it'll throw an exception.

The fix is to use their kIsWeb constant workaround:

import 'package:flutter/foundation.dart' show kIsWeb;


if (!kIsWeb && Platform.isAndroid) {