I have the following function but with this error: Notice: Undefined variable: rating. hoa can I fix it?

function save_comment_meta_rating($comment_id){
    if(!empty($_POST['rating']))
        $rating = sanitize_text_field($_POST['rating']);
        add_comment_meta($comment_id,'rating',$rating);

        // Then update the average rating.
        update_post_avg_rating( $comment_id );
}
add_action('comment_post','save_comment_meta_rating');  

Thanks