Yes, absolutely! And I appreciate you taking the time to go through the spec so carefully and identify these cases, and then to make a validator, which could be very helpful for the community. I’m sorry if anything in my reply came off as confrontational!
You’re right, and I’d be open to a PR that makes this explicit.
Hmmm… I agree with you that that sentence definitely seems to imply that an omitted pagination link is the same as a null one. But I wonder if that’s intentional or if it’s a bug (and, if it’s a bug, what we can do about it, if anything).
If it’s intentional, it seems very inconsistent to me since, even for other links, an omitted link probably wouldn’t be the same as a null one. For example, an omitted "self" link would presumably just mean that a "self" link wasn’t provided, whereas a null "self" link, if such a thing were allowed, would mean that “there exists no URI at which this individual resource object can be accessed”.
All of this, I think, is very closely related to the contradiction identified in #887, which shows that these cases may have been overlooked a bit, and we have to figure out what to do about them.