Non-respondents list: undefined variable $hiddenfields

[MartinGauk]

The code in show_nonrespondents.php tries to read from an undefined variable $hiddenfields.

https://github.com/PoetOS/moodle-mod_questionnaire/blob/5509c94f97c672a290db15aac7960b1b7c4a456e/show_nonrespondents.php#L214:L225

Actually, I wanted to hide the last access column and found this issue.

[mchurchward]

Weird. That file was added back in 2.4 as part of https://tracker.moodle.org/browse/CONTRIB-4058. Those fields have been there since then. I need to see if they are supposed to be doing something important.

[mchurchward]

I'm pretty sure that is supposed to ensure that fields configured as "hidden" on the site (admin/settings.php?section=userpolicies) are not exported. But apparently is was never implemented correctly.
It should have code like:
$hiddenfields = array_filter(explode(',', $CFG->hiddenuserfields));
and
has_capability('moodle/course:viewhiddenuserfields', $context);