Automate insertion of Image Alt text with RM focus keyword

Hi all

I have read the KB for automate insertion of focus keyword as image alt with Image attribute pro..

But can someone please edit the below code to update IMAGE ALT as FOCUS KEYWORD only for those images not having IMAGE ALT TAG

add_filter('wp_get_attachment_image_attributes', 'change_attachement_image_attributes', 20, 2);
function change_attachement_image_attributes( $attr, $attachment ) {
// Get post parent
$parent = get_post_field( 'post_parent', $attachment);

// Get post type to check if it's product
$type = get_post_field( 'post_type', $parent);
if( $type != 'product' ){
    return $attr;
}

/// Get title
$title = get_post_field( 'post_title', $parent);

if( $attr['alt'] == ''){
    $attr['alt'] = $title;
    $attr['title'] = $title;
}

return $attr;
}