public static List<Optional<FileReference>> toFileReferences(List<OptionalPathNode> pathNodes) {
        List<Optional<FileReference>> fileReferences = new ArrayList<>();
        for (OptionalPathNode pathNode : pathNodes)
            fileReferences.add(pathNode.getFileReference());
        return fileReferences;
    }
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