You need to show the exact expression information that is returned and indicate which line is throwing it to get better help. So for now I can only guess that you're getting a NullPointerException as you never initialize the result List<String>.
For instance, I would change this:
ps: I added code tags to your post to help make it readable. The forum FAQ's will show you how to do this yourself: UseCodeTags
ps2: Please let me be the first to welcome you to JavaRanch!