optional path parameter will always send placeholder via swagger UI

[whchi]

When I create swagger doc with "optional path param" it will always send the placeholder {id}

.post(
    '/folders/:id?',
    async ({ params, body }) => {
      const { id } = params;
...
}, {
      params: t.Object({
        id: t.Optional(t.String()),
      }),
}

the id will always be encodeURIComponent('{id}')

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the API works fine using curl so it should be this package's bug