private static boolean isEmptyOptionalPath(Map.Entry<String, ?> entry, ConfigPayloadBuilder fileEntry) {
        return entry.getValue() instanceof ConfigDefinition.OptionalPathDef && fileEntry.getValue() == null;
    }
Registers user configured files for a producer for file distribution.
config-model/src/main/java/com/yahoo/vespa/model/filedistribution/UserConfiguredFiles.java