Flutter 在MobX依赖项的空安全版本上运行build_runner时出错

我在一个Flutter项目中试用MobX，我参考了一个示例，但我提高了版本，这样我就可以练习使用空安全性进行编码。它一直在工作，直到我运行pub升级。运行build_runner时开始出现以下错误：

D:\projects\flutter_mobx_base_code>flutter pub run build_runner clean
Failed to precompile build_runner:build_runner:
/D:/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-1.6.0/lib/src/error/best_practices_verifier.dart:1600:40: Error: Getter not found: 'topLevelVariable'.
      return kinds.contains(TargetKind.topLevelVariable);
                                       ^^^^^^^^^^^^^^^^
/D:/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-1.6.0/lib/src/error/best_practices_verifier.dart:2024:23: Error: Getter not found: 'topLevelVariable'.
      case TargetKind.topLevelVariable:
                      ^^^^^^^^^^^^^^^^
/D:/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-1.6.0/lib/src/error/best_practices_verifier.dart:2024:23: Error: Type 'dynamic' of the case expression is not a subtype
 of type 'TargetKind' of this switch expression.
 - 'TargetKind' is from 'package:meta/meta_meta.dart' ('/D:/flutter/.pub-cache/hosted/pub.dartlang.org/meta-1.3.0/lib/meta_meta.dart').
      case TargetKind.topLevelVariable:
                      ^
/D:/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-1.6.0/lib/src/error/best_practices_verifier.dart:2001:13: Context: The switch expression is here.
    switch (this) {
            ^

这些是我的依赖项：

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^1.0.2
  mobx: ^2.0.0
  flutter_mobx: ^2.0.0
  mobx_codegen: ^2.0.0
  provider: 5.0.0

dev_dependencies:
  build_runner: ^1.12.2
  flutter_test:
    sdk: flutter

环境：
sdk:“>=2.12.0=2.1.0
environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.2
  mobx: ^0.1.2
  flutter_mobx: ^0.1.1
  mobx_codegen: ^0.1.0+1
  provider: ^1.6.1


dev_dependencies:
  flutter_test:
    sdk: flutter
  build_runner: ^1.3.0