[flutter_tools] handle NPE in list views method(#59626)

Fixes #59608

The VmService getter can be null, handle that in the listViews method. NNBD when

packages/flutter_tools/lib/src/resident_runner.dart

@@ -841,9 +841,14 @@ abstract class ResidentRunner {
 
   /// List the attached flutter views.
   Future<List<FlutterView>> listFlutterViews() async {
-    return (await Future.wait(
-      flutterDevices.map((FlutterDevice d) => d.vmService.getFlutterViews()))
-    ).expand((List<FlutterView> views) => views).toList();
+    final List<List<FlutterView>> views = await Future.wait(<Future<List<FlutterView>>>[
+      for (FlutterDevice device in flutterDevices)
+        if (device.vmService != null)
+          device.vmService.getFlutterViews()
+    ]);
+    return views
+      .expand((List<FlutterView> viewList) => viewList)
+      .toList();
   }
 
   /// Write the SkSL shaders to a zip file in build directory.

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -1044,6 +1044,16 @@ void main() {
     expect(fakeVmServiceHost.hasRemainingExpectations, false);
   }));
 
+  testUsingContext('listViews handles a null VM service', () => testbed.run(() async {
+    final FlutterDevice device = FlutterDevice(mockDevice, buildInfo: BuildInfo.debug);
+    final ResidentRunner residentRunner = HotRunner(
+      <FlutterDevice>[device],
+    );
+
+    expect(await residentRunner.listFlutterViews(), isEmpty);
+  }));
+
+
   testUsingContext('ResidentRunner debugDumpApp calls flutter device', () => testbed.run(() async {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
     await residentRunner.debugDumpApp();