How to use the @marblejs/middleware-io.t.union function in @marblejs/middleware-io

(n): n is t.Branded => n >= 0,
  'Positive'
);

type Positive = t.TypeOf;

export const articleSchema = t.type({
  title: t.string,
  markdown: t.string,
  html: t.string,
  tags: t.array(t.string),
  slug: t.string,
  published: t.boolean,
  publishedAt: t.union([t.string, t.null]),
  posterUrl: t.union([t.string, t.null]),
  metaTitle: t.union([t.string, t.null]),
  metaDescription: t.union([t.string, t.null]),
  reactions: t.type({
    types: t.type({
      unicorn: t.type({ count: Positive }),
      heart: t.type({ count: Positive }),
      mark: t.type({ count: Positive }),
    }),
  }),
  lang: t.union([t.literal(ArticleLanguage.FR), t.literal(ArticleLanguage.EN)]),
});

export type ArticlePayload = t.TypeOf;

export const articleValidator$ = requestValidator$({ body: articleSchema });

export const createQuery = (opts: CollectionQueryValidatorOpts) =>
  t.partial({
    sortBy: t.union(opts.sortBy.map(s => t.literal(s)) as any),
    sortDir: t.union([
      t.refinement(t.union([t.string, t.number]), n => Number(n) === SortDir.ASC, 'SortDir.ASC'),
      t.refinement(t.union([t.string, t.number]), n => Number(n) === SortDir.DESC, 'SortDir.DESC'),
    ]),
    limit: t.refinement(t.union([t.string, t.number]), n => Number(n) >= 0, 'number.0+'),
    page: t.refinement(t.union([t.string, t.number]), n => Number(n) >= 1, 'number.1+'),
  });

const Positive = t.brand(
  t.number,
  (n): n is t.Branded => n >= 0,
  'Positive'
);

type Positive = t.TypeOf;

export const articleSchema = t.type({
  title: t.string,
  markdown: t.string,
  html: t.string,
  tags: t.array(t.string),
  slug: t.string,
  published: t.boolean,
  publishedAt: t.union([t.string, t.null]),
  posterUrl: t.union([t.string, t.null]),
  metaTitle: t.union([t.string, t.null]),
  metaDescription: t.union([t.string, t.null]),
  reactions: t.type({
    types: t.type({
      unicorn: t.type({ count: Positive }),
      heart: t.type({ count: Positive }),
      mark: t.type({ count: Positive }),
    }),
  }),
  lang: t.union([t.literal(ArticleLanguage.FR), t.literal(ArticleLanguage.EN)]),
});

export type ArticlePayload = t.TypeOf;

export const articleValidator$ = requestValidator$({ body: articleSchema });