From a103627aa5618b83360b79a07fa971ba9f41bc75 2015-03-28 20:39:24
From: Min RK <benjaminrk@gmail.com>
Date: 2015-03-28 20:39:24
Subject: [PATCH] Backport PR #8176: Fixes bug that would show "null" as the reason in the don't leave dialog

IE treats null as a string and displays it.  Instead simply return.  Fix verified in Chrome, FireFox, and IE 10.

---

diff --git a/IPython/html/static/notebook/js/notebook.js b/IPython/html/static/notebook/js/notebook.js
index 5f572ad..3e40ceb 100644
--- a/IPython/html/static/notebook/js/notebook.js
+++ b/IPython/html/static/notebook/js/notebook.js
@@ -301,9 +301,8 @@ define(function (require) {
                     return "Unsaved changes will be lost.";
                 }
             }
-            // Null is the *only* return value that will make the browser not
-            // pop up the "don't leave" dialog.
-            return null;
+            // IE treats null as a string.  Instead just return which will avoid the dialog.
+            return;
         };
     };