Dart APIunself_modelJsonReftoJson toJson method Null safety Map<String, dynamic> toJson() inherited Implementation Map<String, dynamic> toJson() => throw _privateConstructorUsedError; unself_model unself_model JsonRef toJson method JsonRef class Constructors fromJson ref union Properties hashCode runtimeType Methods getScheme map mapOrNull maybeMap maybeWhen noSuchMethod toJson toString useId when whenOrNull Operators operator ==