whenOrNull<TResult extends Object?>  method 
- @optionalTypeArgs
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( String $type, @AtUriConverter()  AtUri uri,  String cid,  String name, @ListPurposeConverter()  ListPurpose purpose,  String? avatar,  int? listItemCount, @LabelConverter()  List<Label>? labels, @ListViewerStateConverter()  ListViewerState? viewer,  DateTime? indexedAt,  Map<String, dynamic>? $unknown)?  $default,) {final _that = this;
switch (_that) {
case _ListViewBasic() when $default != null:
return $default(_that.$type,_that.uri,_that.cid,_that.name,_that.purpose,_that.avatar,_that.listItemCount,_that.labels,_that.viewer,_that.indexedAt,_that.$unknown);case _:
  return null;
}
}