Error in NextJS getStaticProps when destructuring property 'currentPost' as it is null.

error - pages/[slug].tsx (171:10) @ getStaticProps
TypeError: Cannot destructure property 'currentPost' of '(intermediate value)' as it is null.
  169 |   })
  170 |
> 171 |   const { currentPost, previousPost, nextPost } = await getClient().fetch(
      |          ^
  172 |     postsTest,
  173 |     {
  174 |       slug: params?.slug,

const { currentPost, previousPost, nextPost } = await getClient().fetch(
    postsTest,
    {
      slug: params?.slug,
    }
  )

export const postsTest = groq`
*[_type == "post" && slug.current == $slug]{
  "currentPost": {
    ${postFields}
  },
  "previousPost": *[_type == "post" && ^.publishedAt > publishedAt]|order(publishedAt desc)[0]{title,slug},
  "nextPost": *[_type == "post" && ^.publishedAt < publishedAt]|order(publishedAt asc)[0]{title,slug}
}|order(publishedAt)[0]
`

*[_type == "post"]{
  title,publishedAt,
  "previous": 
  coalesce(*[_type == "post" && ^.publishedAt > publishedAt && false]|order(publishedAt desc)[0]{title,publishedAt}, {}),
  "next": 
coalesce(*[_type == "post" && ^.publishedAt < publishedAt]|order(publishedAt asc)[0]{title,publishedAt}, {})
}|order(publishedAt)

<http://localhost:3000/2021-fcs-playoffs-semifinal-schedule-is-set>

undefined is not an object (evaluating 'currentPost.title')