Undefined Property Error from Block.tpl.php

Whenever I saved a node, I got the following error:

Notice: Undefined property: stdClass::$subject in include() (line 48 of /var/www/html/drupal-7.4-essentials/sites/all/themes/om/core/tpl/block.tpl.php).

I copied the theme's default block.tpl.php into my site's subtheme of OM and I modified line 48 as follows:

Original line 48:

<?php if ($block->subject): ?>

Modified line 48:

<?php if (isset($block->subject) && ($block->subject)): ?>

My modification eliminated the error. I believe that the $block->subject variable is not set because I defined the block with a View and override the title, leaving the title blank.