Repeated enum does not honor ignoreUnknownFields

Consider following snippet of code:

import 'dart:convert';

import 'response.pb.dart';

void main() {
  final response = Response()
    ..repeatedEnumList.addAll([EnumType.ENUM_TYPE_C, EnumType.ENUM_TYPE_B])
    ..singleEnumValue = EnumType.ENUM_TYPE_A;

  final json = response.toProto3Json() as Map<String, dynamic>;
  print(json);
  final serverAndClientInSync = Response.create()..mergeFromProto3Json(json);

  // WORKS
  final json2 = json;
  json2['singleEnumValue'] = 'ENUM_TYPE_CLIENT_UNAWARE';
  print(json2);
  final worksForUpgradedSingleField = Response.create()
    ..mergeFromProto3Json(json2, ignoreUnknownFields: true);

  // FAILS
  final json3 = json;
  json3['repeatedEnumList'][0] = 'ENUM_TYPE_CLIENT_UNAWARE';
  print(json3);
  final failsForUpgradedRepeatedEnumField = Response.create()
    ..mergeFromProto3Json(json3, ignoreUnknownFields: true);
}

Output

{repeatedEnumList: [ENUM_TYPE_C, ENUM_TYPE_B], singleEnumValue: ENUM_TYPE_A}
{repeatedEnumList: [ENUM_TYPE_C, ENUM_TYPE_B], singleEnumValue: ENUM_TYPE_CLIENT_UNAWARE}
{repeatedEnumList: [ENUM_TYPE_CLIENT_UNAWARE, ENUM_TYPE_B], singleEnumValue: ENUM_TYPE_CLIENT_UNAWARE}
Unhandled exception:
type 'Null' is not a subtype of type 'EnumType' of 'element'
#0      PbList.add (package:protobuf/src/protobuf/pb_list.dart)
#1      _mergeFromProto3Json.recursionHelper.<anonymous closure> (package:protobuf/src/protobuf/proto3_json.dart:385:24)
#2      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:625:13)
#3      _mergeFromProto3Json.recursionHelper (package:protobuf/src/protobuf/proto3_json.dart:338:14)
#4      _mergeFromProto3Json (package:protobuf/src/protobuf/proto3_json.dart:416:3)
#5      GeneratedMessage.mergeFromProto3Json (package:protobuf/src/protobuf/generated_message.dart:267:7)
#6      main (package:enums/enums.dart:26:7)
#7      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:296:19)
#8      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:189:12)

Full Code Snippet: https://github.com/Anushi1998/DartProtobufBug/

In case of single enum field, unknown value is ignored but for repeated enums it tried to add null. If we can avoid adding null here it will support backward compatability for repeated enums too. Happy to send a patch if this approach works.

google / protobuf.dart

Repeated enum does not honor ignoreUnknownFields #849

Output