public ConfigInstance.Builder toConfigBuilder(ConfigPayload payload) {
        ConfigInstance.Builder builder = getRootBuilder();
        ConfigPayloadApplier<?> creator = new ConfigPayloadApplier<>(builder, pathAcquirer, urlDownloader);
        creator.applyPayload(payload);
        return builder;
    }
Create a ConfigBuilder from a payload, based on the <code>clazz</code> supplied.

@param payload a Payload to be transformed to builder
@return a ConfigBuilder
config/src/main/java/com/yahoo/vespa/config/ConfigTransformer.java