the client doesn't have to provide it.

                But when using `Item` for output, for a response body, `tags` is always
                available because it has a default value, even if it's just an empty
                list. So, the client should be able to always expect it.

                In this case, there would be two different schemas, one for input and
                another one for output.

                have their default values. This is different from
                `response_model_exclude_defaults` in that if the fields are set,
                they will be included in the response, even if the value is the same
                as the default.

                When `True`, default values are omitted from the response.

                Read more about it in the