From 782915cc52fdefaf9656ead85063d1b71b9d72e7 Mon Sep 17 00:00:00 2001
From: Walter Bender <walter@sugarlabs.org>
Date: Sat, 17 Jul 2010 15:39:01 +0000
Subject: more robust error checking

---
diff --git a/tautils.py b/tautils.py
index c7587c4..e7888ea 100644
--- a/tautils.py
+++ b/tautils.py
@@ -429,7 +429,7 @@ def uncollapse_forks(top, looping=False):
 def collapse_stack(top):
     """ Hide all the blocks between the sandwich top and sandwich bottom. """
     # First uncollapse any nested stacks
-    if top.spr == None:
+    if top == None or top.spr == None:
         return
     uncollapse_forks(top)
     _hit_bottom = False
--
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