PHP Notice: Undefined index: additional_class

Hi, I have been getting loads of errors coming through on my error_log.

PHP Notice: Undefined index: additional_class in /home/mamutov/data/www/lampapo.ru/templates/gk_mystore/html/modules.php on line 73

Can you please tell how to fix it?

For all notice information please turn off the display errors option in your PHP configuration which is recommended for Joomla.

This was causing a huge number of errors in my apache/plesk error logs.
In the file indicated on the line indicated (in my case /gk_postnote/html/modules.php on line 19) add an "@" to the $attrib at the above line :

<div class="moduletable<?php echo $params->get('moduleclass_sfx'); ?><?php echo @$attribs['additional_class']; ?>">

This should tell the server not to populate the 'additional_class' if it is empty. As indicated here:
http://php.net/manual/en/language.operators.php

At any rate it has removed hundreds of errors an hour in my logs.

C