Fix NullPointerException in XML.toString(object, tagName)

Setting version date to match commit date.

Author: stleary

XML.java

@@ -30,7 +30,7 @@ of this software and associated documentation files (the "Software"), to deal
  * This provides static methods to convert an XML text into a JSONObject,
  * and to covert a JSONObject into an XML text.
  * @author JSON.org
- * @version 2015-10-14
+ * @version 2015-10-18
  */
 public class XML {