Error while add UUID to config while Join

I am trying to add the UUID to the config once the player join, but it come out errors.. why?

Error Log:
http://pastebin.com/EFxnCkeB


Code:
@EventHandler
public void onPlayerJoin(PlayerJoinEvent e){

Player player = e.getPlayer();

player.sendMessage("Welcome");

e.setJoinMessage("Welcome");
List<String> playerconfig = plugin.getPlayerConfig().getStringList("Players");

playerconfig.add(player.getUniqueID());

plugin.getPlayerConfig().set("Players", playerconfig);

plugin.

 

@Choohan
If you do not know how to read the error message, please read this thread:
https://bukkit.org/threads/how-to-r...ubleshoot-your-own-plugins-by-yourself.32457/

The issue is that either:

1. the plugin is null.
2. The player's config is null
3. The stringlist is null.

To fix the issue, figure out what is null and figure out why it is null.

 

JoinListener - http://pastebin.com/hPAm5MDS
Mainclass - http://pastebin.com/9WQrUiwH
Player.yml - http://pastebin.com/La6g93pR

Can you help out me?

 

@Choohan You lack basic Java knowledge and conventions, this is why this error occurs. The onEnable only exists in your main class, you never set plugin, UUID != String.

Please read:
https://sites.google.com/site/tecnowizardplugindevelopment/java/not-ready-for-bukkit

 

You never define your plugin in your JoinListener,