This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Does it work when you comment out the call to sort, and does the call to sort work if you run the same code from the console? Do you know the exact line in your code that calls the non-succesful sort? Is there anything on that line that possible could be null? Well... I don't have the code, so I am trying to make you debug it and solve it yourself. ;-)