team picker plugin error

Hello, I am trying to make this plugin to opens a GUI and allows the player to pick a team and they are assigned that team with matching leather armour, but when I try to run the command I get this error


Here is the plugin code

Code:

package com.trobanko.teampicker;

import java.util.ArrayList;
import java.util.List;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Color;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.inventory.meta.LeatherArmorMeta;
import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin implements Listener {

    public Inventory inv;
  
    @Override
    public void onEnable() {
        this.getServer().getPluginManager().registerEvents(this, this);
    }
  
    @Override
    public void onDisable() {
      
    }
  
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (label.equalsIgnoreCase("changeteam")) {
            if (!(sender instanceof Player)) {
                sender.sendMessage("Console may not execute this command");
                return false;
            }
            Player player = (Player) sender;
            player.openInventory(inv);
            return true;
        }
        return false;
    }
  
  
    @EventHandler()
    public void onClick(InventoryClickEvent event) {
        if (!event.getInventory().equals(inv))
            return;
        if (event.getCurrentItem() == null) return;
        if (event.getCurrentItem().getItemMeta() == null) return;
        if (event.getCurrentItem().getItemMeta().getDisplayName() == null) return;
      
        event.setCancelled(true);
      
        Player player = (Player) event.getWhoClicked();
      
        if (event.getSlot() == 0) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.BLUE);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");     
        }
        if (event.getSlot() == 1) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.RED);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
      
        }        if (event.getSlot() == 2) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.GREEN);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
      
        }        if (event.getSlot() == 3) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.PURPLE);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
      
        }        if (event.getSlot() == 4) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.ORANGE);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
      
        }        if (event.getSlot() == 5) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.LIME);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
      
        }        if (event.getSlot() == 6) {
            ItemStack[] armor = player.getEquipment().getArmorContents();
            armor = changeColor(armor, Color.AQUA);
            player.getEquipment().setArmorContents(armor);
            player.sendMessage(ChatColor.GOLD + "Team has been changed");
        }
        if (event.getSlot() == 8) {
            player.closeInventory();
        }
        return;
    }
  
    public ItemStack[] changeColor(ItemStack[] a, Color color) {
        for (ItemStack item : a) {
            try {
                if (item.getType() == Material.LEATHER_BOOTS || item.getType() == Material.LEATHER_CHESTPLATE ||
                        item.getType() == Material.LEATHER_HELMET || item.getType() == Material.LEATHER_LEGGINGS) {
                    LeatherArmorMeta meta = (LeatherArmorMeta) item.getItemMeta();
                    meta.setColor(color);
                    item.setItemMeta(meta);
                }
              
            }
                catch (Exception e) {
                  
                }
            }
      
      
      
        return a;
    }
  
    public void createInv() {
        inv = Bukkit.createInventory(null, 9,ChatColor.AQUA + "" + ChatColor.BOLD + "Select Team");
      
        ItemStack item = new ItemStack(Material.BLUE_CONCRETE);
        ItemMeta meta = item.getItemMeta();
      
        meta.setDisplayName(ChatColor.DARK_BLUE + "BLUE TEAM");
        List<String> lore = new ArrayList<String>();
        lore.add(ChatColor.GRAY + "Click to join this team");
        meta.setLore(lore);
        item.setItemMeta(meta);
        inv.setItem(0, item);
      
        item.setType(Material.RED_CONCRETE);
        meta.setDisplayName(ChatColor.DARK_RED + "RED TEAM");
        item.setItemMeta(meta);
        inv.setItem(1, item);
      
        item.setType(Material.GREEN_CONCRETE);
        meta.setDisplayName(ChatColor.DARK_GREEN + "GREEN TEAM");
        item.setItemMeta(meta);
        inv.setItem(2, item);
      
        item.setType(Material.PURPLE_CONCRETE);
        meta.setDisplayName(ChatColor.DARK_PURPLE + "PURPLE TEAM");
        item.setItemMeta(meta);
        inv.setItem(3, item);
      
        item.setType(Material.ORANGE_CONCRETE);
        meta.setDisplayName(ChatColor.GOLD + "ORANGE TEAM");
        item.setItemMeta(meta);
        inv.setItem(4, item);
      
        item.setType(Material.LIME_CONCRETE);
        meta.setDisplayName(ChatColor.GREEN + "LIME TEAM");
        item.setItemMeta(meta);
        inv.setItem(5, item);
      
        item.setType(Material.CYAN_CONCRETE);
        meta.setDisplayName(ChatColor.BLUE + "CYAN TEAM");
        item.setItemMeta(meta);
        inv.setItem(6, item);
      
        item.setType(Material.BARRIER);
        meta.setDisplayName(ChatColor.RED + "" + ChatColor.BOLD + "Close menu");
        lore.clear();
        meta.setLore(lore);
        item.setItemMeta(meta);
        inv.setItem(8, item);
      
    }
}
[B]

Here is the error code when you type in the command
[/B]

Code:

org.bukkit.command.CommandException: Unhandled exception executing command 'changeteam' in plugin TeamPicker v1.0
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:149) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at org.bukkit.craftbukkit.v1_16_R2.CraftServer.dispatchCommand(CraftServer.java:756) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.PlayerConnection.handleCommand(PlayerConnection.java:1697) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.PlayerConnection.a(PlayerConnection.java:1540) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.PacketPlayInChat.a(PacketPlayInChat.java:47) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.PacketPlayInChat.a(PacketPlayInChat.java:1) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:19) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.TickTask.run(SourceFile:18) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.executeTask(SourceFile:144) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.executeNext(SourceFile:118) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.MinecraftServer.ba(MinecraftServer.java:941) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.MinecraftServer.executeNext(MinecraftServer.java:934) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.awaitTasks(SourceFile:127) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.MinecraftServer.sleepForTick(MinecraftServer.java:918) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.MinecraftServer.w(MinecraftServer.java:850) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at net.minecraft.server.v1_16_R2.MinecraftServer.lambda$0(MinecraftServer.java:164) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at java.lang.Thread.run(Thread.java:832) [?:?]
Caused by: java.lang.NullPointerException
        at org.bukkit.craftbukkit.v1_16_R2.inventory.CraftContainer.getNotchInventoryType(CraftContainer.java:125) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at org.bukkit.craftbukkit.v1_16_R2.entity.CraftHumanEntity.openInventory(CraftHumanEntity.java:298) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        at com.trobanko.teampicker.Main.onCommand(Main.java:43) ~[?:?]
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[spigot.jar:git-Spigot-b5a13e6-a939fbd]
        ... 18 more

Line 43 is:

Code:

 player.openInventory(inv);

 

the inventory is null, where do you call the #createInv() method?