private static ModelReference createModelReference(Optional<String> id, Optional<String> url, Optional<String> path, DeployState state) {
        var fileRef = path.map(p -> state.getFileRegistry().addFile(p));
        return ModelReference.unresolved(id, url.map(UrlReference::valueOf), fileRef);
    }
Expands a model config value into regular config values.
config-model/src/main/java/com/yahoo/vespa/model/container/xml/ModelIdResolver.java