Eval()'error with sample code from your website

Hi,

Sorry, I am a little tired that there is most of the time an error when I tried your code from the website. I have an filed advanced added. Use this sample : https://docs.metabox.io/fields/file-advanced/ and again an error :

Warning: Invalid argument supplied for foreach() in /home/stagingechopper/public_html/wp-content/plugins/oxygen/component-framework/components/classes/code-block.class.php(115) : eval()'d code on line 5

Maybe I am not the best developer but why there is always happens with the samples?

<?php

$field_id = 'ws-dp--voorwaarden_pdf';
$files = rwmb_meta($field_id);
foreach ( $files as $file ) {
    ?>
    <a>"><?php echo $file['name']; ?></a>
    <?php
}

?>