Issue on Themes

Good evening,
I updated my version of WP to 6.0, first I deactivated the plugins and then reactivated one by one and updated those too, the site is reachable and works correctly but when I try to access some pages of the site I get the following error message :

Warning: Creating default object from empty value in /home/vc4y0518/public_html/wp-content/themes/ati/functions.php on line 315

Specifically this is what is present in line 315:

function close_comments( $posts ) {
	if ( !is_single() ) { return $posts; }
	if ( time() - strtotime( $posts[0]->post_date_gmt ) > ( 30 * 24 * 60 * 60 ) ) {
		$posts[0]->comment_status = 'closed';
		$posts[0]->ping_status    = 'closed';
	}
	
	return $posts;

Can you help me?
Thank you