Doing destructive exploratory testing I found this on JMX console:

Using a filter as ":foo" or "foo:foo" I'm getting "HTTP Status 500"

javax.management.MalformedObjectNameException: Invalid character ',' in key part of property
javax.management.ObjectName.construct(ObjectName.java:459)
javax.management.ObjectName.<init>(ObjectName.java:1304)
org.jboss.jmx.adaptor.control.Server.getDomainData(Server.java:72)
org.jboss.jmx.adaptor.html.HtmlAdaptorServlet.displayMBeans(HtmlAdaptorServlet.java:181)
org.jboss.jmx.adaptor.html.HtmlAdaptorServlet.processRequest(HtmlAdaptorServlet.java:94)
org.jboss.jmx.adaptor.html.HtmlAdaptorServlet.doPost(HtmlAdaptorServlet.java:82)
javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)