From a3b73cd3111efa9019c207527185edd0b5caeff3 Mon Sep 17 00:00:00 2001
From: Kris Maglione <maglione.k@gmail.com>
Date: Thu, 14 Jul 2011 01:26:52 -0400
Subject: [PATCH] Closes issue #597.

---
 common/content/buffer.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/common/content/buffer.js b/common/content/buffer.js
index 34e6f832..68867029 100644
--- a/common/content/buffer.js
+++ b/common/content/buffer.js
@@ -741,7 +741,7 @@ var Buffer = Module("buffer", {
      */
     findScrollable: function findScrollable(dir, horizontal) {
         function find(elem) {
-            while (!(elem instanceof Element) && elem.parentNode)
+            while (elem && !(elem instanceof Element) && elem.parentNode)
                 elem = elem.parentNode;
             for (; elem && elem.parentNode instanceof Element; elem = elem.parentNode)
                 if (Buffer.isScrollable(elem, dir, horizontal))
@@ -771,7 +771,7 @@ var Buffer = Module("buffer", {
                         doc.documentElement);
         }
         let doc = this.focusedFrame.document;
-        return elem || doc.body || doc.documentElement;
+        return dactyl.assert(elem || doc.body || doc.documentElement);
     },
 
     /**