whenOrNull<TResult extends Object?>  method 
- @optionalTypeArgs
- TResult? $default(- num? minimumOsVersion
 
A variant of when that fallback to returning null
It is equivalent to doing:
switch (sealedClass) {
  case Subclass(:final field):
    return ...;
  case _:
    return null;
}
Implementation
@optionalTypeArgs
TResult? whenOrNull<TResult extends Object?>(
  TResult? Function(num? minimumOsVersion)? $default,
) {
  final _that = this;
  switch (_that) {
    case _IOSPlatformConstraints() when $default != null:
      return $default(_that.minimumOsVersion);
    case _:
      return null;
  }
}