Drupal : Notice: Undefined index: Return-Path in DefaultMailSystem->mail()

Notice: Undefined index: Return-Path in DefaultMailSystem->mail() (line 101 of C:\xampp\htdocs\Drupal\sis\modules\system\system.mail.inc).
Solution :
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You have problem on "site_mail" row in variable table. Maybe you change its value.
This is site_mail row:  |'site_mail'   |'s:20:\"emsiemhong@gmail.com\";'|
For more information go to link below:
https://drupal.org/node/131737
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