The ErrorHandler interface is only designed for Exception and its subclasses, but the hierarchy is rooted at Throwable. Especially some 500 errors are of type Error.
I had an instance where I was confronted with the default Jetty error page, showing the whole stacktrace because Pippos dispatch only catches Exception and not Throwable.
There might be some research of reasonable behaviour needed, but as Jetty is handling Error types, pippo should probably as well.