`conditionalByType` ignores part of the result when validation is missing

[ntvangoor]

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Bug report

conditionalByType ignores part of the result in a specific scenario.
When one type (e.g. 'heroSection') has its own parser, but another (e.g. 'block') does not, then the result for the latter is ignored during parsing.
This happens because conditionalParser returns an empty object in this case.

This does not work:

conditionalByType({
  block: { // result is { _type: 'block' }
    children: true,
    style: true,
    listItem: true,
    markDefs: true,
    level: true,
  },
  heroSection: (heroSection) => ({
    title: true,
    description: true,
    photos: heroSection.field("photos[]").project((photo) => ({
      src: photo.field("image").field("asset").deref().field("url"),
      alt: true,
      caption: true,
    })),
    columns,
  })
})

But this does:

conditionalByType({
  block: { // result is { _type: 'block', children: ..., style: ..., etc... }
    children: true,
    style: q.string(),
    listItem: true,
    markDefs: true,
    level: true,
  },
  heroSection: (heroSection) => ({
    title: true,
    description: true,
    photos: heroSection.field("photos[]").project((photo) => ({
      src: photo.field("image").field("asset").deref().field("url"),
      alt: true,
      caption: true,
    })),
    columns,
  })
})