Problems when writing addon for Skript.

[mmcheng55]

I am having some issues with calling the Skript API. I was writing a new effect called SupplyChestClickedEffect and it did not work. Spigot are able to call the onEnable method and I did not get any error when I was using the Skript API, but it just did not work. Nothing happened even the addon is not registered. Here are my source codes:

M04Plugin.java

package tech.mmcheng55.plugin;

import ch.njol.skript.Skript;
import ch.njol.skript.SkriptAddon;
import org.bukkit.Bukkit;
import org.bukkit.plugin.java.JavaPlugin;
import tech.mmcheng55.java.addon.effects.SupplyChestClickedEffect;

import java.io.IOException;

public class M04Plugin extends JavaPlugin {
    private static M04Plugin instance;
    private static SkriptAddon addonInstance;

    public M04Plugin() {
        if (instance == null) {
            instance = this;
        } else {
            throw new IllegalStateException();
        }
    }

    public static M04Plugin getInstance() {
        if (instance == null) {
            throw new IllegalStateException();
        }
        return instance;
    }

    public static SkriptAddon getAddonInstance() {
        if (addonInstance == null) {
            addonInstance = Skript.registerAddon(getInstance());
            Bukkit.getLogger().info(addonInstance.toString());
        }
        return addonInstance;
    }

    @Override
    public void onEnable() {
        Skript.registerEffect(SupplyChestClickedEffect.class, "supply %player% at %block%");

        try {
            getAddonInstance().loadClasses("tech.mmcheng55.java.addon", "effects");
        } catch (IOException err) {
            Bukkit.getLogger().info(err.getMessage());
            err.printStackTrace();
        }
        Bukkit.getLogger().info("[LOADED]!!PRJP[QWEUR9WEURFPASJ");
    }
}

SupplyChestClickedEvent.java:

package tech.mmcheng55.java.addon.effects;

import ch.njol.skript.Skript;
import ch.njol.skript.lang.Effect;
import ch.njol.skript.lang.Expression;
import ch.njol.skript.lang.ExpressionType;
import ch.njol.skript.lang.SkriptParser;
import ch.njol.util.Kleenean;
import org.bukkit.event.Event;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import tech.mmcheng55.addon.elements.KtSupplyChestClickedEffect;

public class SupplyChestClickedEffect extends Effect {
    static {
        Skript.registerEffect(SupplyChestClickedEffect.class,  "supply %player% at %block%");
    }

    @Override
    protected void execute(@NotNull Event event) {
        KtSupplyChestClickedEffect.Companion.execute(event);
    }

    @NotNull
    @Override
    public String toString(@Nullable Event event, boolean debug) {
        return KtSupplyChestClickedEffect.Companion.toString(event, debug);
    }

    @Override
    public boolean init(@NotNull Expression<?>[] expressions, int matchedPattern, @NotNull Kleenean isDelayed, @NotNull SkriptParser.ParseResult parseResult) {
        return KtSupplyChestClickedEffect.Companion.init(expressions, matchedPattern, isDelayed, parseResult);
    }
}