def get_path_param_names(path: str) -> set[str]:
    return set(re.findall("{(.*?)}", path))


_invalid_args_message = (
    "Invalid args for response field! Hint: "
    "check that {type_} is a valid Pydantic field type. "
    "If you are using a return type annotation that is not a valid Pydantic "

    if origin is Union or origin is UnionType:
        at_least_one_scalar_sequence = False
        for arg in get_args(annotation):
            if field_annotation_is_scalar_sequence(arg):
                at_least_one_scalar_sequence = True
                continue
            elif not field_annotation_is_scalar(arg):
                return False
        return at_least_one_scalar_sequence

    if origin is not None:
        for arg in get_args(annotation):
            if lenient_issubclass(arg, (BaseModel, Enum)) and arg not in known_models:
                known_models.add(arg)
                if lenient_issubclass(arg, BaseModel):
                    get_flat_models_from_model(arg, known_models=known_models)
            else:
                get_flat_models_from_annotation(arg, known_models=known_models)

        type_annotation = annotated_args[0]
        fastapi_annotations = [
            arg
            for arg in annotated_args[1:]
            if isinstance(arg, (FieldInfo, params.Depends))
        ]
        fastapi_specific_annotations = [
            arg
            for arg in fastapi_annotations
            if isinstance(
                arg,
                (
                    params.Param,

        @app.get("/")
        def read_root() -> Union[Response, None]:
            return Response(content="Foo")  # pragma: no cover

    assert "valid Pydantic field type" in e.value.args[0]
    assert "parameter response_model=None" in e.value.args[0]


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {