Solved IllegalArgumentException: Plugin cannot be null - Menu

Hey, I'm a beginner at Java and when I try to open a menu when a player join the server I get the error "IllegalArgumentException: Plugin cannot be null", I don't know how to fix it could you help me please ?

This is my Main class:

Code:java

import org.bukkit.event.Listener;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;
 
public class Main extends JavaPlugin implements Listener {
    @SuppressWarnings("unused")
    private Main plugin;
 
    // Actions au chargement
    @Override
    public void onEnable() {
        plugin = this;
        PluginManager pm = getServer().getPluginManager();
        pm.registerEvents(new Join(), this);
    }
 
    // Actions à  la fermeture
    @Override
    public void onDisable() {
    }
 
}

And my join class:

Code:java

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.scheduler.BukkitScheduler;
 
public class Join implements Listener {
    private Main plugin;
 
    @EventHandler
        public void onJoin(final PlayerJoinEvent event){
            BukkitScheduler scheduler = Bukkit.getServer().getScheduler();
            scheduler.scheduleSyncDelayedTask(plugin, new Runnable() {
                @Override
                public void run() {
                    Player player = event.getPlayer();
                    Inventory inventory = Bukkit.getServer().createInventory(null, 9, ChatColor.GOLD +  "Menu");
                    player.openInventory(inventory);
                }
            }, 20L);
    }
}

Thanks in advance

 

I seriously need to put this in my signature because I say it a lot. Please learn and understand Java before you start making plugins. Java is the language you are using when you develop plugins. Bukkit is just an API. It's a lot easier to learn Java first then learn an API rather than attempting to understand both simultaneously.

As for your error, your plugin variable it null because you never initialized it.

 

I have corrige your code sorry for my english i am french.

 

Merci beaucoup ça marche nickel je ne m'attendais pas à autant d'aide !