It was present when I run as `mvn jetty:run`. It was not present when I deploy openmrs.war to the tomcat server.
https://www.dropbox.com/s/xheyot1rq6et63b/trailing-slash-example.png

Looks like it depends on the web server's implementation. So it is safer to have a slash before WEB-INF. And it is consistent with the rest of the WebModuleUtil.