Fix typescript error useSearchParams returns ReadonlyURLSearchParams | null with pages

[frano-m]

See https://nextjs.org/docs/app/api-reference/functions/use-search-params:

Good to know:
If an application includes the /pages directory, useSearchParams will return ReadonlyURLSearchParams | null. The null value is for compatibility during migration since search params cannot be known during pre-rendering of a page that doesn't use getServerSideProps