TF-831: add set forward to module

forward/lib/forward/converter/forward_id_nullable_converter.dart

@@ -0,0 +1,13 @@
+import 'package:forward/forward/forward_id.dart';
+import 'package:jmap_dart_client/jmap/core/id.dart';
+import 'package:json_annotation/json_annotation.dart';
+
+class ForwardIdNullableConverter implements JsonConverter<ForwardId?, String?> {
+  const ForwardIdNullableConverter();
+
+  @override
+  ForwardId? fromJson(String? json) => json != null ? ForwardId(id: Id(json)) : null;
+
+  @override
+  String? toJson(ForwardId? object) => object?.id.value;
+}