From cf0fe5faf986efabe8a791e9c771eeb0dc376226 Mon Sep 17 00:00:00 2001
From: Hixie <github.com@spam.hixie.ch>
Date: Fri, 2 Oct 2015 15:27:11 -0700
Subject: [PATCH] Assert that App(routes) is not null.

This is probably a sign that you're using fn2 still.
---
 packages/flutter/lib/src/widgets/app.dart | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/packages/flutter/lib/src/widgets/app.dart b/packages/flutter/lib/src/widgets/app.dart
index 79f9bbab10..64eb172acf 100644
--- a/packages/flutter/lib/src/widgets/app.dart
+++ b/packages/flutter/lib/src/widgets/app.dart
@@ -32,7 +32,15 @@ class App extends StatefulComponent {
     this.theme,
     this.routes,
     this.onGenerateRoute
-  }): super(key: key);
+  }): super(key: key) {
+    assert(() {
+      'The "routes" argument to App() is required.';
+      'This might be a sign that you have not upgraded to our new Widgets framework.';
+      'For more details see: https://groups.google.com/forum/#!topic/flutter-dev/hcX3OvLws9c';
+      '...or look at our examples: https://github.com/flutter/engine/tree/master/examples';
+      return routes != null;      
+    });
+  }
 
   final String title;
   final ThemeData theme;