There is a missing include line of code on this page. The include is for the DataAssist Helper file. This is the line of code that is missing from the top of the page:
<?php require_once("../WA_DataAssist/WA_AppBuilder_PHP.php"); ?>
I'm including an updated copy of this page that has the code in place. Thanks for pointing this out, I have logged this issue so it can be corrected.