public static Map<String, Optional<FileReference>> toFileReferenceMap(Map<String, OptionalPathNode> map) {
        Map<String, Optional<FileReference>> ret = new LinkedHashMap<>();
        for (Map.Entry<String, OptionalPathNode> e : map.entrySet()) {
            ret.put(e.getKey(), e.getValue().getFileReference());
        }
        return ret;
    }
Represents a 'path' in a {@link ConfigInstance}, usually a filename, can be optional

@author hmusum
config-lib/src/main/java/com/yahoo/config/OptionalPathNode.java