[Plugin: comments] No Author Comment URL

Hi, I was wondering if there was a code to prevent the author link from rediercting to the post, if they haven’t entered a URL in the comment field?

Here’s the code I’m using:

<p>By <a href="<?php comment_author_url(); ?>" class="author">
			<?php comment_author(); ?>
			</a></p>

I’m hoping that if they don’t have an author URL, it could not link to anything? Any help is appreciated.

http://wordpress.org/extend/plugins/comments/