As solution I can see using HttpServletRequestWrapper instead of dealing
directly with the HttpServletRequest passed by the container.
This way we can provide custom implementation of HttpServletRequestWrapper
that overrides javax.servlet.ServletRequestWrapper.getCharacterEncoding()
and if
I'm not sure if this is severe or not, but I think there's a gap in the
implicit assumptions underlying WicketFilter.checkCharacterEncoding():
It seems the author's intention was to guarantee a postcondition of
servletRequest.getCharacterEncoding() != null,
but this postcondition does not
