anchor.diff:        'nullable': instance.nullable,
       };
   
  -T _$enumDecode<T>(Map<T, dynamic> enumValues, dynamic source) {
  +T _$enumDecode<T>(
  +  Map<T, dynamic> enumValues,
  +  dynamic source, {
  +  T unknownValue,
  +}) {
     if (source == null) {
       throw ArgumentError('A value must be provided. Supported values: '
           '${enumValues.values.join(', ')}');
     }
  -  return enumValues.entries
  -      .singleWhere((e) => e.value == source,
  -          orElse: () => throw ArgumentError(
  -              '`$source` is not one of the supported values: '
  -              '${enumValues.values.join(', ')}'))
  -      .key;
  +
  +  final value = enumValues.entries
  +      .singleWhere((e) => e.value == source, orElse: () => null)
  +      ?.key;
  +
  +  if (value == null && unknownValue == null) {
  +    throw ArgumentError('`$source` is not one of the supported values: '
  +        '${enumValues.values.join(', ')}');
  +  }
  +  return value ?? unknownValue;
   }
   
  -T _$enumDecodeNullable<T>(Map<T, dynamic> enumValues, dynamic source) {
  +T _$enumDecodeNullable<T>(
  +  Map<T, dynamic> enumValues,
  +  dynamic source, {
  +  T unknownValue,
  +}) {
     if (source == null) {
       return null;
     }
  -  return _$enumDecode<T>(enumValues, source);
  +  return _$enumDecode<T>(enumValues, source, unknownValue: unknownValue);
   }
   
  -const _$FieldRenameEnumMap = <FieldRename, dynamic>{
  +const _$FieldRenameEnumMap = {
     FieldRename.none: 'none',
     FieldRename.kebab: 'kebab',
     FieldRename.snake: 'snake',
  -  FieldRename.pascal: 'pascal'
  +  FieldRename.pascal: 'pascal',
   };
  
positive.code:     'explicitToJson': 'explicit_to_json',
      'fieldRename': 'field_rename',
      'ignoreUnannotated': 'ignore_unannotated',
      'includeIfNull': 'include_if_null',
    });
  }
  
  
negative.code:       'field_rename',
        'ignore_unannotated',
        'include_if_null',
        'nullable'
      ]);
      final val = JsonSerializable(
        anyMap: $checkedConvert(json, 'any_map', (v) => v as bool),
  