I'm not sure if this package is being maintained any more but a path like //@ (i.e starts with a '/' and contains a @) will make this middleware throw an error.

var pathname = url.parse(req.url).pathname;

The line above will return null which makes the following line throw an error:

var cacheValue = cacheValues(slasher(pathname));

It's a strange edge-case I know but it's something I ran into.