whenOrNull<TResult extends Object?>  method 
- @optionalTypeArgs
- TResult? $default(- String identifier,
- List<LabelValueDefinitionFlag> flags,
- bool configurable,
- LabelPreference defaultSetting,
- String severity,
- String blurs,
- Map<LabelTarget, Map< behaviors,ModerationBehaviorContext, ModerationBehavior> >
- String? definedBy,
 
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 identifier,  List<LabelValueDefinitionFlag> flags,  bool configurable,  LabelPreference defaultSetting,  String severity,  String blurs,  Map<LabelTarget, Map<ModerationBehaviorContext, ModerationBehavior>> behaviors,  String? definedBy)?  $default,) {final _that = this;
switch (_that) {
case _InterpretedLabelValueDefinition() when $default != null:
return $default(_that.identifier,_that.flags,_that.configurable,_that.defaultSetting,_that.severity,_that.blurs,_that.behaviors,_that.definedBy);case _:
  return null;
}
}