Major Description
from this topic
http://apache-wicket.1842946.n4.nabble.com/WicketSessionFilter-and-ignorePaths-in-WicketFilter-td3570291.html
Please, look at the second post (the ignorePaths param is not linked with this issue as the title suggests).
How to reproduce with the quickstart:
1. open localhost:8080 - a wicket test page is displayed.
2. open localhost:8080/external - this is the external servlet that tries to access the wicket session. An exception is thrown.