ErrorPage added to Undertow for the 500 code is not used for the 500 code initiated with the exception.

Example can be found here: https://github.com/isopov/embedded-servlet-container-error-pages/blob/master/src/main/java/com/sopovs/moradanen/errors/UndertowErrorPageCode.java

For both Jetty and Tomcat this case does work: https://github.com/isopov/embedded-servlet-container-error-pages/tree/master/src/main/java/com/sopovs/moradanen/errors