in src/main/java/org/apache/maven/resolver/internal/ant/types/Proxy.java [53:61]
public void setRefid(Reference ref) {
if (host != null || port != 0 || type != null || nonProxyHosts != null) {
throw tooManyAttributes();
}
if (authentication != null) {
throw noChildrenAllowed();
}
super.setRefid(ref);
}