StandardService.getConnectorNames returns an array of nulls. The implementation creates an array of the right size, but the body of the for loop that should populate the array does nothing. Easily verified if you look at the ConnectorNames property of the Catalina:type=Service,serviceName=Catalina mbean. I've seen it while running 5.5.12 and still see the problem in the 5.5.20 sources.
Hups, new Tomcat 5.5 Connector can report there ObjectName. Many thanks to report this Peter Fix at revision 497499.