TF-2298 Update expires time when old token has expired

Signed-off-by: dab246 <tdvu@linagora.com>
(cherry picked from commit fb26afe8f52df6e16476aea8a68f9f92c5c4b001)

fcm/lib/converter/fcm_token_nullable_converter.dart

@@ -0,0 +1,12 @@
+import 'package:fcm/model/fcm_token.dart';
+import 'package:json_annotation/json_annotation.dart';
+
+class FcmTokenNullableConverter implements JsonConverter<FcmToken?, String?> {
+  const FcmTokenNullableConverter();
+
+  @override
+  FcmToken? fromJson(String? json) => json != null ? FcmToken(json) : null;
+
+  @override
+  String? toJson(FcmToken? object) => object?.value;
+}