This can be easily reproduce with following snippet of code:

        // or try "modules/java.base/java/lang/Object.class"
        String path = "/modules/java.base/java/lang/Object.class";
        FileSystem fs = FileSystems.getFileSystem(URI.create("jrt:/"));
        Path classFile = fs.getPath(path);

        System.out.println("Class File Size: " + Files.size(classFile));
        if (Files.size(classFile) <= 0L) throw new RuntimeException("Invalid file size");

I only tested on Linux X64.