PrefsOption<T>  constructor 
- String name,
- T value
Implementation
factory PrefsOption(String name, T value) {
  if (value is bool) {
    return BooleanOption(name, value) as PrefsOption<T>;
  } else if (value is int) {
    return IntegerOption(name, value) as PrefsOption<T>;
  } else if (value is String) {
    return StringOption(name, value) as PrefsOption<T>;
  }
  throw ArgumentError(
      'Only `bool`, `int` and `String` are valid parameter types.');
}