Code Review Request: 7160242: (prefs) Preferences.remove(null) does not throw NPE [macosx]

[Kurchi Subhra Hazra]

Hi,

This change inserts a null check for the key being passed to 
Preferences.remove() on Mac, so that
the method throws a NullPointerException when key is null (according to 
its specification).

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7160242
Webrev: http://cr.openjdk.java.net/~khazra/7160242/webrev.00/ Thanks, 
Kurchi