public void save(Path file) {
        try (BufferedWriter writer = Files.newBufferedWriter(file, StandardCharsets.UTF_8)) {
            writer.write("# LuckPerms UUID lookup cache");
            writer.newLine();
            for (Map.Entry<UUID, String> ent : this.lookupMap.entrySet()) {
                String out = ent.getKey() + ":" + ent.getValue();
                writer.write(out);
                writer.newLine();
            }
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
Gets the most recent username used by a given uuid

@param uuid the uuid to lookup with
@return a username, or null
common/src/main/java/me/lucko/luckperms/common/storage/implementation/file/FileUuidCache.java