XML Parse Errors on NO Output Remote CFC access

OK…probably means I should just go home this late on a Friday but can
anyone tell me why accessing a super simple test page (to prove my complex
page wasn’t broken by something else)


which is simply


XML Parsing Error: no element found
Location: https://www.mysite.ca/cfc/test.cfc?method=test
Line Number 1, Column 1:

as found on another post here adding &returnformat=json to the URL makes
the error go away…but there wasn’t an explanation (and I’m not using it
anywhere else…)

This is the first time I’ve run across this. Other remote calls (ie: via
JS) seem to be working fine…

running Lucee final on 2012r2