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