If encoding specified is null or empty, the basic XML parser will fail to start.

Test:
            String encoding = null; //or ""
            Properties props = new Properties();
            props.put("k1", "foo");
            props.put("k2", "bar");
            
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            try {
                  props.storeToXML(out, null, encoding);
            } catch (Exception e) {
                  //fail
            }

Expected:
        save the properties using default encoding (UTF-8)

Actual:
        NullPointerException when encoding = null
        UnsupportedEncodingException when encoding = ""