Getting a name from a list in config is throwing a NullPointerException

Ok so i'm trying to make a class plugin. When a player types /class (classname) it puts their name in a list and the list gets saved to config. In a command, if I put an if statement to check if the players name is in the config, it throws a NullPointerException when I do the command. Any idea why? I've been trying to get this to work for hours.

Main class:

Code:java

package me.Mxeaez.Classes;
 
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;
 
import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;
 
public class Classes extends JavaPlugin {
 
    Logger myPluginLogger = Bukkit.getLogger();
    MyConfigManager manager;
    MyConfig classConfig;
    public Classes plugin;
 
    @Override
    public void onEnable(){
        new Test(this);
        manager = new MyConfigManager(this);
        classConfig = manager.getNewConfig("Classes.yml", new String[] {"Class Config"});
    }
 
    @Override
    public void onDisable()
    {
    }
 
    List<String> Test = new ArrayList<String>();
 
    public boolean onCommand(CommandSender sender, Command cmd, String commandLabel, String[] args)
    {
        if(sender instanceof Player)
        {
            Player player = (Player) sender;
 
            if(cmd.getName().equalsIgnoreCase("class"))
            {
                if(args.length == 0)
                {
                    player.sendMessage(ChatColor.RED + "-----" + ChatColor.GOLD + "Classes Available" + ChatColor.RED + "-----");
                    player.sendMessage(ChatColor.AQUA + "-Test");
                }
                else if(args.length == 1)
                {
                    if(args[0].equalsIgnoreCase("test"))
                    {
                        if(plugin.classConfig.getString("Classes.Test").contains(player.getName()))
                        {
                            Test.add(player.getName());
                            plugin.classConfig.set("Classes.Test", Test);
                            plugin.classConfig.saveConfig();
                            player.sendMessage(ChatColor.GOLD + "You are now a Test!");
                        }
                    }
                }
            }
        }
        return false;
    }
}
 

The error lines that say NullPointerException and what line number (The line number is the if statement to check if the name is in the config)

Code:

Caused by: java.lang.NullPointerException
        at me.Mxeaez.Classes.Classes.onCommand(Classes.java:52)

And lastly, the config file (I already did the command without the check so it put my name in there)

Code:

Classes:
  Test:
  - iTzMeLokKin
  - iTzMeLokKin
  - iTzMeLokKin

 

Mxeaez You never initialized the plugin variable therefore it is null.