NPE when profiling analyzer

Run `dart --observe:5001 /Users/scheglov/Source/Dart/sdk.git/sdk/pkg/analyzer_cli/bin/analyzer.dart /Users/scheglov/Source/Dart/sdk.git/sdk/pkg/analyzer_cli/bin/analyzer.dart`

```
:5001/HBaRonn3Gdo=/devtools/?uri=ws://127.0.0.1:5001/HBaRonn3Gdo=/ws:1 Unchecked runtime.lastError: Could not establish connection. Receiving end does not exist.
flutter_bootstrap.js:121 Attempting to load DevTools with canvaskit renderer.
js_util_patch.dart:81 Server HTTP API is available, using server for storage.
js_util_patch.dart:81 Version: 2.46.0-dev.0, Renderer: canvaskit
js_util_patch.dart:81 Successfully connected to DTD at: ws://127.0.0.1:52838/xcb9wNTNUXs=
js_util_patch.dart:81 DevTools log level changed to INFO
cK5 @ js_util_patch.dart:81
js_util_patch.dart:81 Attempted to call extension 'ext.flutter.inspector.structuredErrors', but no service with that name exists
js_util_patch.dart:81 readyToResume: (106) Isolate must be paused
cK5 @ js_util_patch.dart:81
js_util_patch.dart:81 Could not time async operation "cpuProfileProcessingTime" because an exception was thrown:
Null check operator used on a null value
TypeError: Cannot read properties of undefined (reading 'd')
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92256:23)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
at bQV.$2$current$parent (http://127.0.0.1:5001/HBaRonn3Gdo=/devtools/main.dart.js:92259:83)
cK5 @ js_util_patch.dart:81
core_patch.dart:296 Uncaught Error: Null check operator used on a null value
at bQV.$2$current$parent (cpu_profile_model.dart:1274:39)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
at bQV.$2$current$parent (cpu_profile_model.dart:1385:9)
js_util_patch.dart:81 [zoneGuarded]: Null check operator used on a null value
../../../lib/src/screens/profiler/cpu_profile_model.dart 1274:39 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame
../../../lib/src/screens/profiler/cpu_profile_model.dart 1385:9 _extension#0|generateStackFramesJson.processStackFrame

cK5 @ js_util_patch.dart:81

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```

Issue に記載されている analyzer profiling コマンドで失敗を再現し、その後、stack trace が generateStackFramesJson.processStackFrame に入る lib/src/screens/profiler/cpu_profile_model.dart の 1274 行目と 1385 行目を調べます。CPU プロファイルの処理中に null 値を追跡し、このコマンドの profiling が null チェックエラーなしで完了することを確認します。

索引モデルが issue の本文から書いたものです。