Custom Uri format throws Malformed exception

[jojojames]

If using ring defaults with:

:absolute-redirects - Any redirects to relative URLs will be turned into redirects to absolute URLs, to better conform to the HTTP spec.

set to true,

Returning something like this:

  {:status 302
   :headers {"Location" (format "blah://blah?abc=%s" abc)}
   :body ""}

Will throw -> java.net.MalformedURLException: unknown protocol: blah

Copied from ring-clojure/ring#306 (comment)