[NoThisIsMe]

That's not the question. The question is: If there are no marbles in a bag, are all marbles in the bag black?

[twiceaday]

Sounds weird when you ask the question that way, but if you ask "is there a non-black marble in the bag?" the answer is clearly no. So the question is more like: Should "all marbles in the bag are black" be exactly equal to "not(is there a non-black marble in the bag)".

[Smaug123]

I think you've misunderstood. The question you posed has an answer implied by the parent's question with n=1.