Display related posts in a widget

Hi,

I try to display related posts in a widget with this php code, but it doesn’t work.
What’s wrong in my code ?

<?php global $wp_query;
if(is_object($wp_query->queried_object) && $wp_query->queried_object->ID)
{
if(function_exists('related_posts')) {
echo "<br /><h4 style='text-transform:uppercase; font-size:16px; font-family: Oswald,arial,Georgia,serif; line-height: 1'><div class='widget-top'>Les chroniques</div></h4><br />";
}
related_posts();
}
?>

https://www.ads-software.com/plugins/yet-another-related-posts-plugin/