TF-48 Create and update object for compose email

model/lib/converter/user_id_converter.dart

@@ -0,0 +1,12 @@
+import 'package:json_annotation/json_annotation.dart';
+import 'package:model/model.dart';
+
+class UserIdConverter implements JsonConverter<UserId, String> {
+  const UserIdConverter();
+
+  @override
+  UserId fromJson(String json) => UserId(json);
+
+  @override
+  String toJson(UserId object) => object.id;
+}