Spring Cacheable unless condition doesn't work

I have developed a REST end-point in Springboot that takes a String ID and responds with a ModelAndView. This end-point is marked with @Cacheable annotation. Now there are two things that can happen at the given end-point.

Case 1: The request ID exists in the DB and yields a URL to which redirection needs to happen. In this case, response should be cached so that upon consecutive requests of the same ID, the result can be served from Cache

Case 2: The requested ID doesn't exist in the DB and thus redirection should happen to a specific URL and no caching should be done in this scenario.

So below is my method

@GetMapping("{id}")
    @Cacheable(value = "url-single", key = "#id", unless = "#result.view!=\"redirect:/notfound\"")
    public ModelAndView redirect(@PathVariable("id") String id, ServletRequest servletRequest,
            ServletResponse servletResponse) {
        HttpServletRequest request = HttpServletRequest.class.cast(servletRequest);
        LOG.info("Redirection request from: {} for Short URL Key: {}", request.getRemoteAddr(), id);
        try {
            Optional<String> originalUrlOptional = urlManagerService.retrieveOriginalUrl(id);
            if (originalUrlOptional.isPresent() && !StringUtils.isEmpty(originalUrlOptional.get())) {
                LOG.info("Found Original URL: {} for Short URL Key: {}", originalUrlOptional.get(), id);
                return new ModelAndView("redirect:https://" + originalUrlOptional.get());
            }

        } catch (NoSuchElementException e) {
            LOG.error("Error while redirecting: {}", e.getMessage(), e);
        }
        return new ModelAndView("redirect:/notfound");
    }

If I understand it correctly from here, the keyword unless in @Cacheable applies to the return type and in order to access any particular member variable of the return type object, we have to refer to it as #result.attributeName <comparison> <value>.

So why isn't anything being stored in my Redis cache? If I remove the unless condition, everything gets stored. Is the condition not correct?