Setting the flag @Freezed(toJson: false) creates an error in the generated freezed files when we define a custom toJson.

[PackRuble]

Describe the bug
Let's assume that we need our own fromJson and toJson definitions for the Model. We set the appropriate flags in the @Freezed(fromJson: false, toJson: false) annotation. However, the generated files produce an error:

// analyzer: Missing concrete implementation of 'Model.toJson'.

class _$ModelImpl implements _Model {
  const _$ModelImpl();

  @override
  String toString() {
    return 'Model()';
  }

  @override
  bool operator ==(Object other) {
    return identical(this, other) ||
        (other.runtimeType == runtimeType && other is _$ModelImpl);
  }

  @override
  int get hashCode => runtimeType.hashCode;
}

To Reproduce

import 'package:freezed_annotation/freezed_annotation.dart';

part 'model.freezed.dart';

@Freezed(fromJson: false, toJson: false)
class Model with _$Model {
  const factory Model() = _Model;

  factory Model.fromJson(Map<String, dynamic> json) => Model();

  Map<String, dynamic> toJson() => {};
}

Expected behavior
Adding a constant private constructor solves this problem, because our toJson method becomes an ordinary method of the Model class directly. So it turns out that we have to proceed according to the documentation Adding getters and methods to our models. Is this probably expected behavior?