[FastAPI docs for JSON Compatible Encoder](https://fastapi.tiangolo.com/tutorial/encoder/).
    """
    custom_encoder = custom_encoder or {}
    if custom_encoder:
        if type(obj) in custom_encoder:
            return custom_encoder[type(obj)](obj)
        else:
            for encoder_type, encoder_instance in custom_encoder.items():
                if isinstance(obj, encoder_type):
                    return encoder_instance(obj)

    encoded_instance = jsonable_encoder(
        instance, custom_encoder={safe_datetime: lambda o: o.strftime("%H:%M:%S")}
    )
    assert encoded_instance["dt_field"] == instance["dt_field"].strftime("%H:%M:%S")

    encoded_instance = jsonable_encoder(
        instance, custom_encoder={datetime: lambda o: o.strftime("%H:%M:%S")}
    )

* Fix typos in docs. PR [734](https://github.com/tiangolo/fastapi/pull/734) by [@bundabrg](https://github.com/bundabrg).
* Fix usage of `custom_encoder` in `jsonable_encoder`. PR [#715](https://github.com/tiangolo/fastapi/pull/715) by [@matrixise](https://github.com/matrixise).