private static void move(final Path source,
                             final Path target) {
        if (Files.isDirectory(target)) {
            // Recurse.
            try (final Stream<Path> children = Files.list(source)) {
                children.forEach(child -> move(child, target.resolve(child.getFileName())));
            } catch (final IOException e) {
                LOGGER.error(e.getMessage(), e);
            }

        } else {
            try {
                Files.move(source, target);
            } catch (final IOException e) {
                LOGGER.error(e.getMessage(), e);
            }
        }
    }
@return A map of index UUIDs to lists of the volumes they use. We'll need both, hence the map.
stroom-legacy/stroom-legacy-db-migration/src/main/java/stroom/legacy/db/migration/V07_00_00_1502__Index.java