‘if while else’ conditional content help required

Hi, I’m trying to create a custom template for a page that shows posts in a specific category, but can’t get the default ‘Sorry, no content found’ message to work when there’s no posts.

Here’s my code:

<?php
/*
Template Name: Events in December
*/
?>
<?php get_header(); ?>

	<div id="dates">
    <ul>
    <?php wp_list_pages('title_li=&child_of=16'); ?>
    <ul>
    </ul>
    </div>

	<div id="body_area">

		<div id="text_left">
		<div class="post" id="post-<?php the_ID(); ?>">
		<div class="entry">

<ul class="activities">
<?php query_posts('category_name=december&showposts=0'); ?>
<?php while (have_posts()) : the_post(); ?>
        <li><a href="<?php the_permalink(); ?>">
          <h1><?php the_title(); ?></h1>
          <h2><?php the_excerpt_rss(); ?></h2>
          </a></li>
        <?php endwhile; ?>
</ul>
			</div>
		</div>
	</div>
    <div id="text_right"><?php get_sidebar(); ?></div>
	</div>
<?php get_footer(); ?>

Any suggestions?