public ConfigPayloadBuilder put(String key) {
            ConfigPayloadBuilder p = new ConfigPayloadBuilder(getStructMapDef(name));
            elements.put(key, p);
            return p;
        }
Create a new map where new values may be added.

@param name Name of map.
@return Map builder supporting adding elements to it.
config/src/main/java/com/yahoo/vespa/config/ConfigPayloadBuilder.java