From 05e21b72919a0d79c953884ea576f2e1f28bd85a Mon Sep 17 00:00:00 2001
From: Qiang Xue <qiang.xue@gmail.com>
Date: Tue, 1 Jul 2014 14:49:41 -0400
Subject: [PATCH] Fixes #4135

---
 framework/db/BaseActiveRecord.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/framework/db/BaseActiveRecord.php b/framework/db/BaseActiveRecord.php
index ede9becef0..365f469985 100644
--- a/framework/db/BaseActiveRecord.php
+++ b/framework/db/BaseActiveRecord.php
@@ -716,7 +716,7 @@ abstract class BaseActiveRecord extends Model implements ActiveRecordInterface
 
         $changedAttributes = [];
         foreach ($values as $name => $value) {
-            $changedAttributes[$name] = $this->_oldAttributes[$name];
+            $changedAttributes[$name] = isset($this->_oldAttributes[$name]) ? $this->_oldAttributes[$name] : null;
             $this->_oldAttributes[$name] = $value;
         }
         $this->afterSave(false, $changedAttributes);