JimfsFileSystemProvider#getFileSystem(URI) and JimfsFileSystemProvider#getPath(URI) just throw exceptions telling you to use FileSystems.getFileSystem(URI) and Paths.get(URI) respectively, but those recommended methods just fall back on calling these ones that throw unconditional exceptions.

Expectation:

You call Paths.get(URI) where the URI has a jimfs scheme and you get a Path object.

Reality:

You get an exception saying This method should not be called directly; use Paths.get(URI) instead.