Well, but if there are incomplete responses, that question could have been left unasnwered, right?

probably so, but that is not the problem in this case.

i don't think stat is related to QuestionTheme currently

probably so, but that is not the problem in this case.

What I am saying is that it can't be removed taht easely as there are situations when that optins shold be shown.
Do you have a sample LSA so we can reproduce and evaluate?

I think this is not a bug. As said, a 'no answer' option is always shown in statistics, because there might be someone who did not answer this one yet, still there is a response.

In 2.6 : we have a difference between is null and empty ?
And we have "not shown" and "not answered" if i didn't make error.

Maybe : start point : "not answered or not shown" for label ?

If this option is deactivated in the questions, no answer is possible BUT it still appears in the statistics.
This makes no sense in terms of usability in the statistics.

If of course one of the other questions this option would be activated, the visibility in the statistics would be comprehensible even if no data are available.

If this option is deactivated in the questions, no answer is possible BUT it still appears in the statistics.

I think there is a typo in the sentence above.
Still, I think I understand.
If the allow "no answer" option is deactivated, still, there could be situations where the question is not shown to participant (participant exiting before question is shows, relevance, ...). In those cases, "no answer" should be OK in statistics.