Code Review Request: 7165118: (prefs) AbstractPreferences.remove(null) does not throw NPE

[Kurchi Hazra]

Hi,

   This is a simple fix to enable AbstractPreferences.remove() to check 
for a null argument and
throw a NullPointerException if required.
   I have also modified test/java/util/prefs/RemoveNullKeyCheck.java to 
cover this case.

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7165118
Webrev: http://cr.openjdk.java.net/~khazra/7165118/webrev.00/

Thanks,
Kurchi