java.lang.RuntimeException: Sentinel calling getObject

I got the following exception:

```java.util.concurrent.CompletionException: java.lang.RuntimeException: Sentinel calling getObject: org.dartlang.vm.service.element.Sentinel@42df8084
at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:331)
at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:346)
at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:632)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2088)
at io.flutter.inspector.EvalOnDartLibrary.lambda$null$0(EvalOnDartLibrary.java:97)
at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:859)
at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:837)
at java.base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)
Caused by: java.lang.RuntimeException: Sentinel calling getObject: org.dartlang.vm.service.element.Sentinel@42df8084
at io.flutter.inspector.EvalOnDartLibrary$3.received(EvalOnDartLibrary.java:236)
at org.dartlang.vm.service.VmService.forwardResponse(VmService.java:788)
at org.dartlang.vm.service.VmServiceBase.processResponse(VmServiceBase.java:630)
at org.dartlang.vm.service.VmServiceBase.processMessage(VmServiceBase.java:437)
at org.dartlang.vm.service.VmServiceBase$1.onMessage(VmServiceBase.java:86)
at de.roderick.weberknecht.WebSocketReceiver.run(WebSocketReceiver.java:65)
```

## Version info

```
[✓] Flutter (Channel stable, v1.17.2, on Mac OS X 10.15.4 19E287, locale en-GB)
• Flutter version 1.17.2 at /Users/sagarsuri/development/flutter
• Framework revision 5f21edf8b6 (5 days ago), 2020-05-28 12:44:12 -0700
• Engine revision b851c71829
• Dart version 2.8.3

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
• Android SDK at /Users/sagarsuri/Library/Android/sdk
• Platform android-29, build-tools 29.0.3
• Java binary at: /Applications/Android
Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build
1.8.0_212-release-1586-b4-5784211)
• All Android licenses accepted.

[✗] Xcode - develop for iOS and macOS
✗ Xcode installation is incomplete; a full installation is necessary for iOS
development.
Download at: https://developer.apple.com/xcode/download/
Or install Xcode via the App Store.
Once installed, run:
sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
sudo xcodebuild -runFirstLaunch
✗ CocoaPods not installed.
CocoaPods is used to retrieve the iOS and macOS platform side's plugin
code that responds to your plugin usage on the Dart side.
Without CocoaPods, plugins will not work on iOS or macOS.
For more info, see https://flutter.dev/platform-plugins
To install:
sudo gem install cocoapods

[!] Android Studio (version 3.6)
• Android Studio at /Applications/Android Studio.app/Contents
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.
• Java version OpenJDK Runtime Environment (build
1.8.0_212-release-1586-b4-5784211)

[!] IntelliJ IDEA Community Edition (version 2020.1.1)
• IntelliJ at /Applications/IntelliJ IDEA CE.app
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.
• For information about installing plugins, see
https://flutter.dev/intellij-setup/#installing-the-plugins

[✓] Connected device (1 available)
• ASUS ZS620KL • J7AAGF06H076S89 • android-arm64 • Android 10 (API 29)

! Doctor found issues in 3 categories
```

Start with the stack trace entries in io.flutter.inspector.EvalOnDartLibrary.java, especially lines 97 and 236, and inspect how the VM service response is handled. Reproduce the reported Flutter 1.17.2 failure if possible; done means the Sentinel response no longer causes this RuntimeException or is handled with a clear diagnostic.

Written by the indexing model from the issue text.