Command Problems

Hey guys, I keep getting an error. I've done plugins similar to this in the past and have never encountered this error. Please help.
Main:

Code:

package me.Ugonnalive.ElytraJousting;

import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin {
   
    @Override
    public void onEnable() {
        getCommand("joust").setExecutor(new Command1());
        Command1.plugin = this;
    }
}

Command1:

Code:

package me.Ugonnalive.ElytraJousting;

import java.util.Collection;

import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scheduler.BukkitRunnable;

public class Command1 implements CommandExecutor {
   

    @Override
    public boolean onCommand(CommandSender sender, Command arg1, String arg2, String[] arg3) {
        if (sender instanceof Player) {
            runnable();
        }
        return true;
    }
   
    static JavaPlugin plugin;
    ItemStack arrow = new ItemStack(Material.ARROW, 1);
    ItemStack crossbow = new ItemStack(Material.CROSSBOW, 1);
    ItemStack sword = new ItemStack(Material.STONE_SWORD, 1);
    ItemStack helmet = new ItemStack(Material.IRON_HELMET, 1);
    ItemStack leggings = new ItemStack(Material.IRON_LEGGINGS, 1);
    ItemStack boots = new ItemStack(Material.IRON_BOOTS, 1);
   
    public void runnable() {
        new BukkitRunnable() {
           
            @Override
            public void run() {
                Collection<? extends Player> players = Bukkit.getOnlinePlayers();
                ItemStack elytra = new ItemStack(Material.ELYTRA, 1);

                for (Player player: players) {
                    player.getInventory().setHelmet(helmet);
                    player.getInventory().setLeggings(leggings);
                    player.getInventory().setBoots(boots);
                    player.getInventory().setChestplate(elytra);
                    player.setGliding(true);
                   
                    if(player.getInventory().getItem(1) != sword) {
                        player.getInventory().setItem(1, sword);
                    }
                    if(player.getInventory().getItem(2) != crossbow) {
                        player.getInventory().setItem(2, crossbow);
                    }
                    if(player.getInventory().getItem(9) != arrow) {
                        player.getInventory().setItem(9, arrow);
                    }

                }
            }   
        }.runTaskTimerAsynchronously(plugin, 0, 1);
    }
}

plugin.yml:

Code:

name: ElytraJousting
main: me.Ugonnalive.ElytraJousting.Main
version: 1.0
author: me
api-version: 1.16
commands:
  glide:
    description: Elytra Jousting.
    usage: /joust

Error:

Code:

[22:06:41] [Server thread/ERROR]: Error occurred while enabling ElytraJousting v1.0 (Is it up to date?)
java.lang.NullPointerException: null
        at me.Ugonnalive.ElytraJousting.Main.onEnable(Main.java:11) ~[?:?]
        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:263) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:351) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:480) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at org.bukkit.craftbukkit.v1_16_R2.CraftServer.enablePlugin(CraftServer.java:494) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at org.bukkit.craftbukkit.v1_16_R2.CraftServer.enablePlugins(CraftServer.java:408) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at net.minecraft.server.v1_16_R2.MinecraftServer.loadWorld(MinecraftServer.java:435) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at net.minecraft.server.v1_16_R2.DedicatedServer.init(DedicatedServer.java:216) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at net.minecraft.server.v1_16_R2.MinecraftServer.w(MinecraftServer.java:808) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at net.minecraft.server.v1_16_R2.MinecraftServer.lambda$0(MinecraftServer.java:164) ~[server.jar:git-Spigot-57bbdd8-b8dd5ec]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_251]

 

Thank You, it worked.