public static ModelReference resolveToModelReference(
            String paramName, Optional<String> id, Optional<String> url, Optional<String> path, Set<String> requiredTags, DeployState state) {
        if (id.isEmpty()) return createModelReference(Optional.empty(), url, path, state);
        else if (state.isHosted())
            return createModelReference(id, Optional.of(modelIdToUrl(paramName, id.get(), requiredTags)), Optional.empty(), state);
        else if (url.isEmpty() && path.isEmpty()) throw onlyModelIdInHostedException(paramName);
        else return createModelReference(id, url, path, state);
    }
Expands a model config value into regular config values.
config-model/src/main/java/com/yahoo/vespa/model/container/xml/ModelIdResolver.java