private Identifiable createFromId(int id) {
            var pair = typeMap.get(id);
            return (pair != null) ? pair.getSecond().get() : null;
        }
Creates an instance of the class mapped to by the given identifier.
@param id The id of the class to create.
@return The instantiated object.
vespajlib/src/main/java/com/yahoo/vespa/objects/Identifiable.java