Nice catch on the repeated word. I'll fix that.

As for how to articulate the edge case, I think it could be accurately described in both ways. Yes, the error is a direct result of the method's searching for a key that isn't there, but the reason it does so is that the smallest key is larger than the number argument. Your way of stating the problem is at the level of implementation; my way is something closer to the user's perspective. I'm happy to use either one in the Changelog. Just let me know which you prefer.