NPE in front-end war during shutdown

In certain rare events:

2008-01-09 13:27:58.046::INFO: Shutdown hook executing
2008-01-09 13:27:58.063::WARN: EXCEPTION
java.lang.NullPointerException
at org.hippoecm.frontend.Main.onDestroy(Main.java:121) <--- line number may not be correct
at org.apache.wicket.Application.internalDestroy(Application.java:889)
at org.apache.wicket.protocol.http.WebApplication.internalDestroy(WebApplication.java:447)
at org.apache.wicket.protocol.http.WicketFilter.destroy(WicketFilter.java:143)
at org.mortbay.jetty.servlet.FilterHolder.destroyInstance(FilterHolder.java:129)
at org.mortbay.jetty.servlet.FilterHolder.doStop(FilterHolder.java:109)
at org.mortbay.component.AbstractLifeCycle.stop(AbstractLifeCycle.java:65)
at org.mortbay.jetty.servlet.ServletHandler.doStop(ServletHandler.java:165)
at org.mortbay.component.AbstractLifeCycle.stop(AbstractLifeCycle.java:65)
at org.mortbay.jetty.handler.HandlerWrapper.doStop(HandlerWrapper.java:129)