Moving all OAuth code and samples to use Storage consistently
diff --git a/samples/oauth2/buzz/buzz.py b/samples/oauth2/buzz/buzz.py
index fe30a32..a009517 100644
--- a/samples/oauth2/buzz/buzz.py
+++ b/samples/oauth2/buzz/buzz.py
@@ -27,7 +27,7 @@
 def main():
   storage = Storage('buzz.dat')
   credentials = storage.get()
-  if not credentials:
+  if credentials is None or credentials.invalid == True:
     flow = OAuth2WebServerFlow(
         client_id='433807057907.apps.googleusercontent.com',
         client_secret='jigtZpMApkRxncxikFpR+SFg',