[mobx_codegen] error with code generation when file has unnamed `extension`

Reproducable code

import 'package:mobx/mobx.dart';

part 'view_model.g.dart';

class ViewModel = _ViewModel with _$ViewModel;

abstract class _ViewModel with Store {
  @observable
  List<int> list = [];
}

extension on int {}

Error

[INFO] Starting Build
[INFO] Updating asset graph completed, took 1ms
[SEVERE] mobx_codegen:mobx_generator on lib/view_model.dart:

Null check operator used on a null value
package:mobx_codegen/src/type_names.dart 32:46            LibraryScopedNameFinder.namesByElement
package:mobx_codegen/src/type_names.dart 137:12           LibraryScopedNameFinder._getNamedElementTypeName
package:mobx_codegen/src/type_names.dart 94:12            LibraryScopedNameFinder._getDartTypeName
dart:_internal                                            ListIterable.toList
package:mobx_codegen/src/type_names.dart 133:56           LibraryScopedNameFinder._getNamedElementTypeName
package:mobx_codegen/src/type_names.dart 94:12            LibraryScopedNameFinder._getDartTypeName
package:mobx_codegen/src/type_names.dart 48:7             LibraryScopedNameFinder.findVariableTypeName
package:mobx_codegen/src/store_class_visitor.dart 100:28  StoreClassVisitor.visitFieldElement
package:analyzer/src/dart/element/element.dart 3110:54    FieldElementImpl.accept
package:analyzer/src/dart/element/element.dart 2491:13    ElementImpl.visitChildren
package:mobx_codegen/src/mobx_codegen_base.dart 85:9      StoreGenerator._generateCodeFromTemplate
package:mobx_codegen/src/mobx_codegen_base.dart 67:13     StoreGenerator._generateCodeForMixinStore
dart:core                                                 Iterable.toSet
package:mobx_codegen/src/mobx_codegen_base.dart 26:68     StoreGenerator.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

[INFO] Running build completed, took 47ms
[INFO] Caching finalized dependency graph completed, took 23ms
[SEVERE] Failed after 74ms

Packages

build_runner: ^2.4.11
mobx_codegen: ^2.6.1
flutter_mobx: ^2.2.1+1
mobx: ^2.3.3+2

Flutter version: 3.22.2 if I add name to extension, it will work fine

extension _intX on int {}

mobxjs / mobx.dart

[mobx_codegen] error with code generation when file has unnamed `extension` #1010