1. Open browser console
2. Visit mw.org Special:Search > Advanced
3. Click [All], [None], toggle individual checkboxes

Result:
All & None buttons have no effect, and enabling individual namespace checkboxes has no effect on which namespaces are searched.

Meanwhile in browser console:

Exception thrown by mediawiki.special.search
TypeError: this.form is null

with ?debug=1

TypeError: this.form is null
https://bits.wikimedia.org/static-1.25wmf12/resources/src/mediawiki.special/mediawiki.special.search.js
Line 53
this.form.method = this.checked ? 'post' : 'get';

In theJS, $checkboxes is an empty array. The jQuery selector

$checkboxes = $( '#powersearch input[id^=mw-search-ns]' );

doesn't work because the <form id="powersearch" ...> closes before the checkboxes and other advanced features.

FWIW in debug mode I get warnings like 'Use of "addCheckboxClickHandlers" is deprecated. Use jquery.checkboxShiftClick instead.'

It also happens on beta labs.

Is there a browser test for advanced search? Do we log Exception thrown in JavaScript code?