build errors in master branch (ComponentEventsTest.destroy)

[Tobias Soloschenko]

Hi all,

before I added the changes of wicket-metrics into the master branch I 
saw that there are test issues:

Before the wicket-metrics changes:
https://ci.apache.org/builders/wicket-master/builds/283/steps/compile/logs/stdio

After the wicket-metrics changes:
https://ci.apache.org/builders/wicket-master/builds/285/steps/compile/logs/stdio

I don't know why there are NullPointerExceptions in 
ComponentEventsTest.destroy.

Any ideas?

kind regards

Tobias