Why !! (double negation operator is used here)? [duplicate]

 const { hotelId } = useParams();

  const { data: hotel } = useQuery(
    "fetchHotelById",
    () => apiClient.fetchHotelById(hotelId || ""),
    {
     enabled: !!hotelId,
    }
  );

Why double negation operator is used here? why not just hotelId?