On line 5 of class Software you create a new Application with the parameterless Constructor. So in this instance, the Application-array apps
holds 4 instances of Application, created in your loadApplications()-method. On line 7 you call getNextApplication() on it, which returns the first entry of the array. Note, that this Application was created with the second constructor (new Application("Aquatint","1.1","Stick Software","","Mike","crocodiles","http://www.sticksoftware.com/","","");
). Therefore it's apps-array is empty, because you don't call loadApplications() in that constructor.
So app on line 10 is null. Bingo.
One mistake, you make, is to reuse the variable app again and again. That way you call getNextApplication() always on a new instance of Application. Try this:
...but don't try it more than 4 times
By the way: what is the intention to hold a list of Applications in Application-class? Shouldn't it rather be a class ApplicationPortfolio or so, to hold the Applications?