randomAlphanumeric function
Implementation
String randomAlphanumeric(int length, {bool isUppercase = false}) {
const String chars = 'abcdefghijklmnopqrstuvwxyz0123456789';
final String pool = isUppercase ? chars.toUpperCase() : chars;
return List<String>.generate(length, (_) => pool[_rnd.nextInt(pool.length)]).join();
}