public <T extends ConfigInstance> void request(JRTConfigSubscription<T> sub) {
        Objects.requireNonNull(sub, "sub cannot be null");
        JRTClientConfigRequest req = JRTConfigRequestFactory.createFromSub(sub);
        doRequest(sub, req);
    }
Requests the config for the {@link com.yahoo.config.ConfigInstance} on the given {@link ConfigSubscription}

@param sub a subscription
config/src/main/java/com/yahoo/config/subscription/impl/JRTConfigRequester.java