@Override
    public Optional<UUID> lookupUniqueId(String username) {
        //noinspection deprecation
        return Optional.ofNullable(getServer().getOfflinePlayer(username)).map(OfflinePlayer::getUniqueId);
    }
The time when the plugin was enabled
bukkit/src/main/java/me/lucko/luckperms/bukkit/LPBukkitBootstrap.java