Wordpress get post thumbnail url

wp-get-post-thumbnail-url.php

<?php

/**
 * Return the post thumbnail URL
 *
 * @param  string             $size      thumbnail size name
 * @param  \WP_Post|int       $post      wordpress post object
 * @return string|boolean                the post thumbnail url, the fallback url or false
 */
function get_post_thumbnail_url($size = 'post-thumbnail', $post = null) {
    if($post === null) {
        global $post;
    } else {
      if(is_numeric($post)) {
        $post = get_post($post);
      }
    }
    if(has_post_thumbnail($post->ID)) {
        $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), $size );
        if($image) {
          return $image[0];
        }
    }
    
    return '';
}