Mysterious NullPointerException

[Jeremy Levy]

I see the following a few times a day, this is with Wicket 1.3.6.  It
results in a 500 being displayed to the user...

2009-06-18 00:53:09,485 ERROR Web [RequestCycle] :
java.lang.NullPointerException

I realize this isn't much to go on, any ideas?

j