Handle collected objects and expired handles more gracefully.

tests/standalone/vmservice/isolate_bad_object_test.dart

Index: tests/standalone/vmservice/isolate_bad_object_test.dart
diff --git a/tests/standalone/vmservice/isolate_bad_object_test.dart b/tests/standalone/vmservice/isolate_bad_object_test.dart
index d22ba641239aa96b6a6b65497a4fdd7d392337e0..8d156f6af6088a9bf44ac40913e5694583343569 100644
--- a/tests/standalone/vmservice/isolate_bad_object_test.dart
+++ b/tests/standalone/vmservice/isolate_bad_object_test.dart
@@ -13,7 +13,7 @@ class NullCollectionTest extends VmServiceRequestHelper {
       super('http://127.0.0.1:$port/$id/objects/50');
 
   onRequestCompleted(Map reply) {
-    Expect.equals('null', reply['type']);
+    Expect.equals('Null', reply['type']);
   }
 }