I believe that's the license key for a paid app on BlackBerry World, previously known as AppWorld. If so, and your app is free, then a 'null' value is nothing to worry about.
The user is reporting "uncaught java exception error" which means your app is triggering an exception somewhere, and not dealing with it gracefully. Ask the user for more detail - what are they doing when this happens? Also, because BlackBerry devices do not let us collect stack traces programmatically, you can walk the user through the process of collecting the stack trace from the uncaught exception, by using the Alt-LGLG method.