But in that case, wouldn't “unknown“ be even better? I'm not a native english speaker, though, so I may miss some fine nuances in the meaning of “none“.
'unknown' is almost like saying "We don't know what should be here", while 'none' is closer to saying "We didn't get passed any information here".
Ultimately, I feel like 'unknown' is more specific, it conveys intent beyond that of 'none'. Such as, it could imply we actually don't know what kind of data 'Opinions' should hold, rather than that there merely happens to be no data to put there.
Cookies in the jar: none
and
Cookies in the jar: unknown