the logic of ungraded

I discovered this problem by accident. I was grading some manually graded essay questions, and accidentally forgot to change the grade of one from zero to 10, but I had added a comment to it. I noticed this as I was saving it, so it wasn't a problem and I changed it, but I noticed that even though I had given the student a comment on the essay, it was still being listed as an ungraded question. In theory, a teacher should be able to give a student a zero on a essay question and it be considered graded. It seems to me that a decision needs to be made about what is considered ungraded. Is it:

1-A question without a comment and a grade of zero? (now it is, and it seems that it should remain this way)

2-A question with a comment but a grade of zero? (now it is, but not sure whether that is proper)

3-A question of any grade but no comment? (do we force teachers to make a comment?)

Maybe the way to solve this is to set the default grade as null rather than zero. Then it will be very clear whether a question has been graded or not.