v3.0-preview.18 出现 The method '[]' was called on null. Tried calling: []("containers")

[VERBOSE-2:ui_dart_state.cc(209)] Unhandled Exception: NoSuchMethodError: The method '[]' was called on null.
Receiver: null
Tried calling: []("containers")
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:68:5)
#1 StackInfo.decode (package:flutter_boost/src/messages.dart:52:31)
#2 NativeRouterApi.getStackFromHost (package:flutter_boost/src/messages.dart:310:24)

#3 FlutterBoostAppState._restoreStackForHotRestart (package:flutter_boost/src/flutter_boost_app.dart:208:19)

环境：
`
flutter_boost:
git:
url: 'https://github.com/alibaba/flutter_boost.git'
ref: 'v3.0-preview.18'
`
[✓] Flutter (Channel unknown, 2.8.1, on macOS 12.2 21D5025f darwin-x64, locale zh-Hans-CN)
• Upstream repository unknown
• Framework revision 77d935af4d (3 周前), 2021-12-16 08:37:33 -0800
• Engine revision 890a5fca2e
• Dart version 2.15.1
• Pub download mirror https://pub.flutter-io.cn
• Flutter download mirror https://storage.flutter-io.cn

[✓] Xcode - develop for iOS and macOS (Xcode 13.2.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• CocoaPods version 1.11.2

[✓] Android Studio (version 4.0)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 51.0.1
• Dart plugin version 193.7547
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

Reproduce the hot-restart failure with flutter_boost v3.0-preview.18 and the Flutter 2.8.1 environment described. Inspect StackInfo.decode and NativeRouterApi.getStackFromHost in package:flutter_boost/src/messages.dart, then _restoreStackForHotRestart in package:flutter_boost/src/flutter_boost_app.dart; done means stack restoration no longer raises this null exception.

Written by the indexing model from the issue text.