iAmAnIntentionalENoticeThatWarnsOfAProblemYouShouldReport in Participant Search

To reproduce this on http://dmaster.demo.civicrm.org/ :

1. Visit /civicrm/event/search?reset=1 to perform a Participant Search.
2. Select an event in the Event Name criteria field (e.g., "Rain Forest Cup Youth Soccer Tournament")
3. Select one status in the Participant Status criteria field (e.g., "Registered")
4. Submit the search form.
5. On the search results page, observe this error:
Notice: Undefined variable: iAmAnIntentionalENoticeThatWarnsOfAProblemYouShouldReport in CRM_Contact_BAO_Query::buildClause() (line 5410 of /srv/buildkit/build/dmaster/sites/all/modules/civicrm/CRM/Contact/BAO/Query.php).

Bonus:
If change the above recipe so that you select two or more values for the Participant Status criteria (e.g., "Registered" and "Attended") in step 3, the same error message appears twice.

BTW, search results appear to be correct, but I haven't done a very thorough check to verify that claim.

I'm happy to help debug this, but the code says "here be dragons" – yikes! What to do?