Does this line do the same thing as before? I thought there was a distinction between `query_set.filter(foo__a='a').filter(foo__b='b')` and `query_set.filter(foo__a='a', foo__b='b')`, namely that the second one requires that the same `foo` matches both queries while the second one doesn't.

In particular I think this query will get all students that have a valid studentregistration (possibly for a different registration type) and a (possibly expired) studentregistration for the matching registration type, which is not what we want?