Flutter Null Safety Migration

我正在try 将我的项目迁移到Flatter空安全版本，我遵循this官方迁移指南.

When I run the second command it says
Package doesn't exist (the Flutter SDK is not available).

我跑的命令

me@My-MacBook-Air my_project % dart --version
Dart SDK version: 2.12.0 (stable) (Thu Feb 25 19:50:53 2021 +0100) on "macos_x64"
me@My-MacBook-Air my_project % dart pub outdated --mode=null-safety
Package doesn't exist (the Flutter SDK is not available).

Flutter doctor 输出

me@My-MacBook-Air my_project % `flutter doctor -v`
Flutter (Channel beta, 2.0.2, on macOS 11.2.3 20D91 darwin-x64, locale en-IN)
    • Flutter version 2.0.2 at /Users/me/flutter
    • Framework revision 8962f6dc68 (9 days ago), 2021-03-11 13:22:20 -0800
    • Engine revision 5d8bf811b3
    • Dart version 2.12.1

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/me/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/me/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.1

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      ? https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      ? https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.51.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.17.0

[✓] Connected device (2 available)
    • macOS (desktop) • macos  • darwin-x64     • macOS 11.2.3 20D91 darwin-x64
    • Chrome (web)    • chrome • web-javascript • Google Chrome 89.0.4389.90

• No issues found!