Thanks for the question! The correct negation for “none” is actually just “not none,” or in other words, “some!” That’s the way you want to think about negations, just stick the word “not” in front of whatever you’re negating. So the negation of “all,” for example, is “not all,” or “some are not.” The negation of “some,” however, is “not some,” or “none.” And it makes sense—what’s the opposite of nothing? Well, something! Doesn’t have to be everything.
Hope this helps! Feel free to ask any other questions that you might have.