never call methods on a variable which could be null. For comparison, your code fragment should have read
Code:
if (INS[Counter] == null)
but if you were testing to see if it were equal to something else, it should have been this:
Code:
if ("aString".equals(INS[Counter]))
because the literal "aString" can never be null, it will always always be "aString". Keep this in mind and you'll save yourself loads of trouble with hard to read error messages and stack traces.
HTH
B.