public static Optional<String> getChildValue(Element e, String name) {
        var child = getChild(e, name);
        if (child == null) return Optional.empty();
        return Optional.of(getValue(child));
    }
@return the value of child with the given name, empty string if no value, or empty if no child with name
vespajlib/src/main/java/com/yahoo/text/XML.java