Chapter SRV.12.8 of the
Servlet 2.4 specification covers this. In particular "An authorization constraint that names no roles indicates that access to the constrained requests must not be permitted under any circumstances." and in SRV.12.8.1 you'll find that "The special case of an authorization constraint that names no roles shall combine with any other constraints to override their affects and cause access to be precluded."
However, it seems that in the past this was not always implemented corrrectly by
Tomcat (which is the reference implementation for the Servlet Spec);
see here.
Also, if you post questions like these, please
QuoteYourSources.