Request for approval: 7055065 NullPointerException when sorting JTable with empty cell

[Jonathan Lu]

Hi all,

Here's a request of porting fix 7055065 back to JDK7, could you please 
help to review?

Bug: http://bugs.sun.com/view_bug.do?bug_id=7055065

Change set: http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/dfa2ea47257d

Thread where it was reviewed:
http://mail.openjdk.java.net/pipermail/swing-dev/2012-April/001981.html

Thanks,
Jonathan