Up till now (see original ticket), we (I) disabled VaadinSession's default error handler by setting it to null.

This was probably done so that only our own error handler (which is registered on the UI, not the session) deals with Vaadin errors, avoiding the big fat red boxes. Our AdmincentralErrorHandler sends message to the pulse.

Now, although it doesn't even prevent the big fat red boxes to show up, it has the definite disadvantage to swallow Vaadin internal errors like PaintExceptions — those that are obviously not handled at UI level, because they occur while the UIDL response is being written.

We need to either restore the session-level DefaultErrorHandler, which is enough for the exceptions to appear in the logs, or add a specific handler of our own instead. Just anything but null really.