Deploying Next JS on Vercel

21:00:59.874  	> Build error occurred
21:00:59.876  	Error: Invalid `paths` value returned from getStaticPaths in /[slug].
21:00:59.876  	`paths` must be an array of strings or objects of shape { params: [key: string]: string }
21:00:59.877  	    at buildStaticPaths (/vercel/workpath0/node_modules/next/dist/build/utils.js:16:1065)
21:00:59.877  	    at processTicksAndRejections (internal/process/task_queues.js:97:5)
21:00:59.877  	    at async Object.isPageStatic (/vercel/workpath0/node_modules/next/dist/build/utils.js:26:612) {
21:00:59.877  	  type: 'Error'
21:00:59.877  	}

export async function getStaticProps ({ params = {}, preview = false }) {
  const { slug } = params
  const { page: pageData } = await getClient(preview).fetch(query, {
    slug
  })

  return {
    props: { preview, pageData, slug }
  }
}

export async function getStaticPaths () {
  const routes = await getClient()
    .fetch(`*[_type == "route" && defined(slug.current)]{
    "params": {"slug": slug.current}
  }`)

  return {
    paths: routes || null,
    fallback: true
  }
}