Subclasses generated with Freezed are detected as InvalidType or crashing the code generator

[YukiAttano]

Describe the bug
Subclasses generated with Freezed are detected as InvalidType or crashing the code generator

To Reproduce
Having a freezed class like this:

import "package:freezed_annotation/freezed_annotation.dart";

part 'some.freezed.dart';

part "some.g.dart";

@freezed
class Some with _$Some {

  const Some._();

  const factory Some.one() = SomeOne;

  const factory Some.two() = SomeTwo;

  factory Some.fromJson(Map<String, dynamic> json) => _$SomeFromJson(json);
}

And a Retrofit class like this:

part "some_repo.g.dart";

@RestApi()
abstract class SomeRepo {
  factory SomeRepo(Dio dio, {String baseUrl}) = _SomeRepo;

  @GET("Some")
  Future<SomeOne> some(int id);
}

will break the generator with a line

package:source_gen/src/type_checker.dart 215:74 TypeChecker.isSuperTypeOf

Null check operator used on a null value
package:source_gen/src/type_checker.dart 215:74             TypeChecker.isSuperTypeOf
package:retrofit_generator/src/generator.dart 914:51        RetrofitGenerator._generateRequest
package:retrofit_generator/src/generator.dart 426:17        RetrofitGenerator._generateMethod.<fn>
package:code_builder/src/specs/method.g.dart 323:33         _$MethodBuilder.update
package:code_builder/src/specs/method.g.dart 38:29          new _$Method
package:retrofit_generator/src/generator.dart 378:12        RetrofitGenerator._generateMethod
package:retrofit_generator/src/generator.dart 234:21        RetrofitGenerator._parseMethods.<fn>
dart:core                                                   List.addAll
package:built_collection/src/list/list_builder.dart 98:14   ListBuilder.addAll
package:retrofit_generator/src/generator.dart 117:19        RetrofitGenerator._implementClass.<fn>
package:code_builder/src/specs/class.g.dart 345:33          _$ClassBuilder.update
package:code_builder/src/specs/class.g.dart 40:28           new _$Class
package:retrofit_generator/src/generator.dart 103:26        RetrofitGenerator._implementClass
package:retrofit_generator/src/generator.dart 88:12         RetrofitGenerator.generateForAnnotatedElement
package:source_gen/src/generator_for_annotation.dart 61:30  GeneratorForAnnotation.generate
package:source_gen/src/builder.dart 342:33                  _generate
dart:async                                                  Stream.toList.<fn>
package:source_gen/src/builder.dart 107:9                   _Builder._generateForLibrary
package:source_gen/src/builder.dart 99:5                    _Builder.build

passing a list type List<SomeOne> instead of SomeOne as the return type for the call generates the following function (the return type is not detected and InvalidType is used):

@override
  Future<List<InvalidType>> some(int id) async {
    final _extra = <String, dynamic>{};
    final queryParameters = <String, dynamic>{};
    final _headers = <String, dynamic>{};
    const Map<String, dynamic>? _data = null;
    final _options = _setStreamType<List<InvalidType>>(Options(
      method: 'GET',
      headers: _headers,
      extra: _extra,
    )
        .compose(
          _dio.options,
          'Some',
          queryParameters: queryParameters,
          data: _data,
        )
        .copyWith(
            baseUrl: _combineBaseUrls(
          _dio.options.baseUrl,
          baseUrl,
        )));
    final _result = await _dio.fetch<List<dynamic>>(_options);
    late List<InvalidType> _value;
    try {
      _value = _result.data!
          .map((dynamic i) => InvalidType.fromJson(i as Map<String, dynamic>))
          .toList();
    } on Object catch (e, s) {
      errorLogger?.logError(e, s, _options);
      rethrow;
    }
    return _value;
  }

Notice: Passing the super type "Some" instead of "SomeOne" or "SomeTwo" is not a problem but also not a solution as this would be the wrong return type.

Expected behavior
I would expect that the code generator generates a working code with the defined type as long as it is json-serializable.