The "sys" module is now called "util" and it is not really necessary in this example.
The filename requested was "Summerfäscht.jpg", what encodes to "Summerf 30X1.D78P-10654scht.jpg". The reconversion was not made in node-static. This lead to a 404 despite the files availability.
The comparison between the root path and the filepath did reject all files. (At least if you .server('.') ). Fixed by resolving each path to an absolute path with path.resolve() and comparing absolute paths. In addition, this seems to me to be a saver comparison. Possibly reduces the cache memory footprint as the key is now the full path. (Is only true if previously multiple relative paths lead to the same absolute path.)