Display random post custom field

I found and adapted this code from another post on this forum but i need some extra functionallity that i cant work out.

<?php $rand_posts = get_posts('cat=8&numberposts=1&orderby=rand'); foreach( $rand_posts as $post ) : ?>
<a href="<?php the_permalink() ?>" class="test1"><?php echo get_post_meta($post->ID, "testimonial", true); ?></a>
<?php endforeach; ?>

But not every post in category 8 have testimonials so i want to be able to skip the post with no entry. because at the minute i get a blank space when it returns a post with no testiomial.

Thanks!