If Student.getMark(x) returns null, does this mean they haven't taken unit x? E.g, for task 9 we should filter over Students that return null? re u n A t r t r o e h t d n s w o h v a e u i r m n w s o o d s .

You don't need to implement a new iterator for this question as it just returns a single object of type R Consider a helper method that does something to each next() of iterator it