Hello,
phpdocx doesn't throw an Exception in this particular case; a fatal error appears from PHP. All DOCX must contain at least one section (sectPr tag).
An Exception could be added in the class if the following sectPr variable is null:
$sectPr = $sectPrNodes->item(0);
or handle the error in a generic way if you are using PHP 7: https://www.php.net/manual/en/language.errors.php7.php
Using not valid DOCX documents as this case may return unexpected results/errors.
Regards.