wicket-4533 please review

[Peter Ertl]

Hi wicket team,

I would like to fix WICKET-4533 but 6.0.0 is darn close. So could you possibly 
take a look at https://issues.apache.org/jira/browse/WICKET-4533 and tell me if 
it will be okay to commit the patch?

Thanks and best regards
Peter