public String getInstancePropName(String restClientName, String key) {
        if (getNameSpace() == null) {
            throw new NullPointerException("getNameSpace() may not be null");
        }
        return restClientName + "." + getNameSpace() + "." + key;
    }
Create instance with no properties in the specified name space
ribbon-archaius/src/main/java/com/netflix/client/config/DefaultClientConfigImpl.java