added add() codes, main

this doesn't work--i get this error:
Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.compareTo(String.java:1167)
	at OrderedSuperArray.add(OrderedSuperArray.java:14)
	at OrderedSuperArray.main(OrderedSuperArray.java:28)
when i run (it compiles) though