Get the "link_category" value from a link object

Hello, I’ve been reading almost everything about bookmarks on the codex and couldn’t find a reason for my code to be wrong. I need to have an alphabetical list of all my bookmarks with the category they’re in as “class”.
The problem is that, even though I’m sure those links have a category, the “link_category” value is always empty (but i I can get the others values as “link_name”).

here’s the page.
And the code:

<ul>
		<?php
		$links = get_bookmarks( 'orderby=name' );
		foreach($links as $link) :?>

  			<li class="<?php echo $link->link_category; ?>">
  				<?php echo $link->link_name; ?>

			</li>

		<?php endforeach; ?>
	</ul>