PHP: Jika input kosong, maka tidak muncul

MASTER KALAU KOSONG TIDAK MUNCUL
<!-- Let's show our custom fields here -->

sendiri:
<?php
    $my_isbn = get_post_meta( get_the_ID(), 'isbn', true);
        if( ! empty( $my_isbn ) ) {
        echo '<p>ISBN: ' . $my_isbn . '</p>';
    }
?>


digabung:
<?php
    $my_preview = get_post_meta( get_the_ID(), 'preview', true);
    $my_isbn = get_post_meta( get_the_ID(), 'isbn', true);
    if( ! empty( $my_preview ) ) {
        echo '<h3>Download: <a href="' . $my_preview . '" target="_blank">Link</a><h3>';
         }
         if( ! empty( $my_isbn ) ) {
        echo '<p>ISBN: ' . $my_isbn . '</p>';
    }
?>
<!-- End showing our custom fields here -->