Fixing first-chance exception in TodoMVC

pkg/observe/lib/src/path_observer.dart

Index: pkg/observe/lib/src/path_observer.dart
diff --git a/pkg/observe/lib/src/path_observer.dart b/pkg/observe/lib/src/path_observer.dart
index 6e31b558f25235c22a4f31318d2596595073e687..931ee04fd2c6381588017e193269cb5648dcc513 100644
--- a/pkg/observe/lib/src/path_observer.dart
+++ b/pkg/observe/lib/src/path_observer.dart
@@ -171,6 +171,10 @@ class PathObserver extends ChangeNotifierBase {
 }
 
 _getObjectProperty(object, property) {
+  if (object == null) {
+    return null;
+  }
+
   if (object is List && property is int) {
     if (property >= 0 && property < object.length) {
       return object[property];