com.sun.tools.javac.file.Locations.ModulePathLocationHandler.ModulePathIterator#inferModuleName reads:

// --
if (p.getFileName().toString().endsWith(".jar") && fsInfo.exists(p)) {
    URI uri = URI.create("jar:" + p.toUri());
// --

This code was introduced recently and was modelled after this snippet just
a few lines below:

// --
           if (p.getFileName().toString().endsWith(".jmod")) {
                    try {
                        FileSystem fs = fileSystems.get(p);
                        if (fs == null) {
                            URI uri = URI.create("jar:" + p.toUri());
// --

Both of these are problematic as they construct a URI that will fail
with a MalformedURLException should a URL ever be constructed
from the URI.

At the moment this bug is latent (harmless) since these faulty states are
transient and quickly disposed without triggering any problems/symptoms.

But these should be cleaned up.