@Override
    public Identifiable clone() {
        try {
            return (Identifiable)super.clone();
        } catch (CloneNotSupportedException e) {
            throw (AssertionError)new AssertionError("The cloneable structure has been broken.").initCause(e);
        }
    }
Declares that all subclasses of Identifiable supports clone() by _not_ throwing CloneNotSupported exceptions.

@return A cloned instance of this.
@throws AssertionError Thrown if a subclass does not implement clone().
vespajlib/src/main/java/com/yahoo/vespa/objects/Identifiable.java