handle no question set on reference_sheet#optional?
handle no question set on reference_sheet#optional?

this makes it a bit easier to test reference-related stuff since you
don't have to set up a proper question on a page with a question sheet

CruGlobal/qe,CruGlobal/fe,CruGlobal/qe,CruGlobal/fe,CruGlobal/fe,CruGlobal/qe