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;
+}

forward/lib/forward/tmail_forward.dart

@@ -1,4 +1,5 @@
 import 'package:forward/forward/converter/forward_id_coverter.dart';
+import 'package:forward/forward/converter/forward_id_nullable_converter.dart';
 import 'package:forward/forward/forward.dart';
 import 'package:forward/forward/forward_id.dart';
 import 'package:json_annotation/json_annotation.dart';
@@ -6,13 +7,14 @@ import 'package:json_annotation/json_annotation.dart';
 part 'tmail_forward.g.dart';
 
 @ForwardIdConverter()
-@JsonSerializable()
+@ForwardIdNullableConverter()
+@JsonSerializable(explicitToJson: true, includeIfNull: false)
 class TMailForward extends Forward {
-  final ForwardId id;
+  final ForwardId? id;
   final bool localCopy;
   final Set<String> forwards;
   TMailForward({
-    required this.id,
+    this.id,
     required this.localCopy,
     required this.forwards,
   });