static Optional<Long> requiredGeneration(HttpRequest req) {
        Optional<String> requiredGeneration = Optional.ofNullable(req.getProperty(REQUIRED_GENERATION));
        return requiredGeneration.map(Long::parseLong);
    }
If the given config is produced by the model at all

@return ok or not
configserver/src/main/java/com/yahoo/vespa/config/server/http/HttpConfigRequest.java