"The question of 'are all crows black' isn't a null hypothesis, but the question 'all crows are black' is. "

Not only is that not a null hypothesis, it isn't even a question. It could well be a hypothesis. It sounds more like an unsupported assertion coming from a standpoint of ignorance. A bit like my saying that all butterflies are red admirals. As someone who knows a bit about crows, I'd be asking "What makes you think that?" There would inevitably be an inadequate answer to that and the line of enquiry would cease forthwith as not being worth pursuing.