* Allow path parameters to have default values (e.g. `None`) and discard them instead of raising an error.
* This allows declaring a parameter like `user_id: str = None` that can be taken from a query parameter, but the same path operation can be included in a router with a path `/users/{user_id}`, in which case will be taken from the path and will be required.
* PR [464](https://github.com/tiangolo/fastapi/pull/464) by [jonathanunderwood](https://github.com/jonathanunderwood).
* Add support for setting a `default_response_class` in the `FastAPI` instance or in `include_router`. Initial PR [467](https://github.com/tiangolo/fastapi/pull/467) by [toppk](https://github.com/toppk).
* Add support for type annotations using strings and `from __future__ import annotations`. PR [451](https://github.com/tiangolo/fastapi/pull/451) by [dmontagu](https://github.com/dmontagu).