public boolean hasNext() {
        /*
         * Don't store a new Iterator until we know the user can't remove() the last returned
         * element anymore. Otherwise, when we remove from the old iterator, we may be invalidating
         * the new one. The result is a ConcurrentModificationException or other bad behavior.
         *
         * (If we decide that we really, really hate allocating two Iterators per cycle instead of

## 0.80.0

### Breaking Changes - Fixes

* 🐛 Fix `response_model` not invalidating `None`. PR [#2725](https://github.com/tiangolo/fastapi/pull/2725) by [@hukkin](https://github.com/hukkin).