Vấn đề về code PHP?

add_action( 'save_post', 'raynoblog_set_featured_image');function raynoblog_set_featured_image() {
    if ( ! isset( $GLOBALS['post']->ID ) )
        return NULL;        
    if ( has_post_thumbnail( get_the_ID() ) )
        return NULL;            
        $args = array(
            'numberposts'    => 1,
            'order'          => 'ASC', // DESC for the last image
            'post_mime_type' => 'image',
            'post_parent'    => get_the_ID(),
            'post_status'    => NULL,
            'post_type'      => 'attachment'
        );          
        $attached_image = get_children( $args );
        if ( $attached_image ) {
            foreach ( $attached_image as $attachment_id => $attachment )
                set_post_thumbnail( get_the_ID(), $attachment_id );
        }           
}