copyWith on a dynamic field is bad cosntructed

[oscarshaitan]

Describe the bug
Having an obj with a dynamic field, the copyWith is generated with no replacement with null like other fields
The Objs with other 2 examples field

// coverage:ignore-file
import 'package:freezed_annotation/freezed_annotation.dart';

part 'test_obj.freezed.dart';

part 'test_obj.g.dart';

@freezed
class TestObj with _$TestObj {
  @JsonSerializable(fieldRename: FieldRename.snake)
  const factory TestObj({
    required String stringRequired,
    String? stringNullable,
    @Default('1') String stringWithDefault,
    required int intRequired,
    int? intNullable,
    @Default(1) int intWithDefault,
    required dynamic dynamicRequired,
    dynamic? dynamicNullable,
    @Default(null) dynamic dynamicWithDefault,
  }) = _TestObj;


  factory TestObj.fromJson(Map<String, dynamic> json) => _$TestObjFromJson(json);

}

The copyWith generted

/// @nodoc
class _$TestObjCopyWithImpl<$Res, $Val extends TestObj>
    implements $TestObjCopyWith<$Res> {
  _$TestObjCopyWithImpl(this._value, this._then);

  // ignore: unused_field
  final $Val _value;
  // ignore: unused_field
  final $Res Function($Val) _then;

  @pragma('vm:prefer-inline')
  @override
  $Res call({
    Object? stringRequired = null,
    Object? stringNullable = freezed,
    Object? stringWithDefault = null,
    Object? intRequired = null,
    Object? intNullable = freezed,
    Object? intWithDefault = null,
    Object? dynamicRequired = null,
    Object? dynamicNullable = null,
    Object? dynamicWithDefault = null,
  }) {
    return _then(_value.copyWith(
      stringRequired: null == stringRequired
          ? _value.stringRequired
          : stringRequired // ignore: cast_nullable_to_non_nullable
              as String,
      stringNullable: freezed == stringNullable
          ? _value.stringNullable
          : stringNullable // ignore: cast_nullable_to_non_nullable
              as String?,
      stringWithDefault: null == stringWithDefault
          ? _value.stringWithDefault
          : stringWithDefault // ignore: cast_nullable_to_non_nullable
              as String,
      intRequired: null == intRequired
          ? _value.intRequired
          : intRequired // ignore: cast_nullable_to_non_nullable
              as int,
      intNullable: freezed == intNullable
          ? _value.intNullable
          : intNullable // ignore: cast_nullable_to_non_nullable
              as int?,
      intWithDefault: null == intWithDefault
          ? _value.intWithDefault
          : intWithDefault // ignore: cast_nullable_to_non_nullable
              as int,
      dynamicRequired: null == dynamicRequired
          ? _value.dynamicRequired
          : dynamicRequired // ignore: cast_nullable_to_non_nullable
              as dynamic,
      dynamicNullable: null == dynamicNullable
          ? _value.dynamicNullable
          : dynamicNullable // ignore: cast_nullable_to_non_nullable
              as dynamic?,
      dynamicWithDefault: null == dynamicWithDefault
          ? _value.dynamicWithDefault
          : dynamicWithDefault // ignore: cast_nullable_to_non_nullable
              as dynamic,
    ) as $Val);
  }
}

Expected behavior
the dynamic should be

dynamicNullable: freezed == dynamicNullable
          ? _value.dynamicNullable
          : dynamicNullable // ignore: cast_nullable_to_non_nullable
              as dynamic,

considering that dynamic is already nullable

in consequence, if I want to reset the dynamic field with null is not resetting the field and returns the new object with the old value

[rrousselGit]

It's low priority to me. If you want this fixed, feel free to make a PR