The old functional view didn't support allow_empty.  I had copied the `get` method from the generic `ListView` which does make use of it (the `allow_empty` functionality comes with `MultipleObjectMixin`), but commented it out as I didn't think it made any sense to raise a 404 when filtering.  But, I had left it commented, so someone could chime in as to whether they thought it was needed.

If a `FilterView` is considered a full replacement for using `ListView` though, then it might be.