This code has a slash at the end of the opening <root> tag, but also has a closing </root> tag.

    private void writeRoot() throws BackingStoreException, IOException {
        bw.write("  <root type=\"");
        if (prefs.isUserNode()) {
            bw.write("user"); 
        } else {
            bw.write("system");
        }
        bw.write("\"/>");
            
        writeRootMap();
        writeNode();
        
        bw.write("  </root>");
        bw.newLine();
    }