Dart APIunself_modelActivitytoJson toJson method Null safety Map<String, dynamic> toJson() inherited Implementation Map<String, dynamic> toJson() => throw _privateConstructorUsedError; unself_model unself_model Activity toJson method Activity class Constructors Activity fromJson Properties accountId appId archiveId copyWith created extra hashCode id labels name runtimeType source sourceId targetId timestamp type updated Methods noSuchMethod toJson toString Operators operator ==