Drupal 7, displaying page custom field with handling null exceptions

 <?php if ($content['field_banner']): ?>
 开发者_如何学JAVA           <div class="proj"><?php print render($content['field_banner']) ?></div>
            <?php endif; ?>

My if condition is not working, if the page doesn't have banner, i am getting an error: Notice: Undefined index: field_banner in include() (line 28 of node.tpl.php

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Maybe a little isset() can make the difference.

<?php if (isset($content['field_banner'])): ?>