@SuppressWarnings("unchecked")
    private static Class<ConfigInstance> configClass(ConfigBuilder builder) {
        return (Class<ConfigInstance>) builder.getClass().getEnclosingClass();
    }
@author Tony Vaagenes
@author gjoranv
@author ollivir
standalone-container/src/main/java/com/yahoo/container/standalone/StandaloneSubscriberFactory.java