Exception-throwing Listener Class

package nightterror6.magicrpg;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

import org.bukkit.Bukkit;
import org.bukkit.DyeColor;
import org.bukkit.Material;
import org.bukkit.enchantments.Enchantment;
import org.bukkit.entity.Player;
import org.bukkit.event.EventException;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.event.inventory.InventoryCloseEvent;
import org.bukkit.event.inventory.InventoryOpenEvent;
import org.bukkit.event.inventory.InventoryType;
import org.bukkit.event.player.PlayerInteractEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

import net.md_5.bungee.api.ChatColor;

public class ScrollEnchantment implements Listener{

	private Main main;
	Inventory ew = Bukkit.createInventory(null, 9, ChatColor.LIGHT_PURPLE + "" + ChatColor.BOLD + "Enchant");

	private final int ITEM_SLOT = 5;
	private final int SCROLL_SLOT = 3;

	private final String paneName  = ChatColor.GRAY + "Enchant an Item with a Scroll";
	private final String confirmName = "" + ChatColor.GREEN + "" + ChatColor.BOLD + "Confirm";

	private ItemStack scroll = null;


	public ScrollEnchantment(Main main) {
		main.getServer().getPluginManager().registerEvents(this,main);
		this.main = main;
	}

	@EventHandler(priority = EventPriority.HIGH)
	public void onPlayerUse(PlayerInteractEvent e) {
		Player p = e.getPlayer();
		Inventory pInv = p.getInventory();
		ItemStack heldItem = p.getItemInHand();
		if(e.getAction().equals(Action.RIGHT_CLICK_AIR) || e.getAction().equals(Action.RIGHT_CLICK_BLOCK)) {
			if(heldItem.getType() == Material.PAPER && heldItem.getItemMeta().hasEnchants()){
				ew.setItem(SCROLL_SLOT, heldItem);
				p.getInventory().remove(heldItem);
				scroll = heldItem;

				ItemStack aestheticItem = new ItemStack(Material.STAINED_GLASS_PANE, 1, DyeColor.GRAY.getWoolData());
				ItemMeta meta = aestheticItem.getItemMeta();
				meta.setDisplayName(paneName);
				aestheticItem.setItemMeta(meta);

				/*
				ItemStack confirm = new ItemStack(Material.STAINED_GLASS_PANE, 1, DyeColor.GREEN.getWoolData());
				ItemMeta confirmMeta = confirm.getItemMeta();
				meta.setDisplayName(confirmName);

				confirm.setItemMeta(confirmMeta);*/

				ItemStack confirmItem = new ItemStack(Material.STAINED_GLASS_PANE, 1, DyeColor.GREEN.getWoolData());
				ItemMeta confirmMeta = confirmItem.getItemMeta();
				confirmMeta.setDisplayName(confirmName);

				ArrayList<String> confirmLore = new ArrayList<String>();
				confirmLore.add(ChatColor.GRAY + "Confirm enchantment");
				confirmMeta.setLore(confirmLore);

				confirmItem.setItemMeta(confirmMeta);

				ew.setItem(0, aestheticItem);
				ew.setItem(1, aestheticItem);
				ew.setItem(2, aestheticItem);
				ew.setItem(4, confirmItem);
				ew.setItem(6, aestheticItem);
				ew.setItem(7, aestheticItem);
				ew.setItem(8, aestheticItem);

				p.openInventory(ew);
			}

		}
		if(e.getAction() == Action.RIGHT_CLICK_BLOCK && e.getClickedBlock().getType() == Material.ENCHANTMENT_TABLE && p.getItemInHand().getType() == Material.PAPER) {
			ItemStack paper = p.getItemInHand();
		}

	}

	@EventHandler(priority = EventPriority.HIGH)
	public void onInventoryClick(InventoryClickEvent e){
		Player p = (Player) e.getWhoClicked();
		Inventory pInv = p.getInventory();
		ItemStack clickedItem = e.getCurrentItem();
		if(clickedItem == null) {
			return;
		}
		Inventory i = e.getInventory();
		final boolean isScroll = clickedItem.getType() == Material.PAPER && clickedItem.getItemMeta().hasEnchants();
		final boolean isPaper = clickedItem.getType() == Material.PAPER && !clickedItem.getItemMeta().hasEnchants();
		if(i.getName().equals(ew.getName())) {
			if(clickedItem.getItemMeta().getDisplayName().equals(paneName) || clickedItem.getItemMeta().getDisplayName().equals(confirmName)) {
				e.setCancelled(true);
			}
			if(isScroll){
				e.setCancelled(true);
				p.closeInventory();
				pInv.addItem(i.getItem(ITEM_SLOT));
				i.removeItem(i.getItem(ITEM_SLOT));
			}
			if(clickedItem.getItemMeta().getDisplayName().equals(confirmName)) {
				ItemStack toEnch = i.getItem(ITEM_SLOT);
				ItemStack enchanter = i.getItem(SCROLL_SLOT);
				if(toEnch.getType() != Material.AIR){

					toEnch.addEnchantments(enchanter.getEnchantments());
					ew.removeItem(enchanter);
					ew.removeItem(toEnch);
					pInv.addItem(toEnch);
					p.closeInventory();
					return;
				}
			}
		}
		if(clickedItem.getItemMeta().getDisplayName().equals(confirmName)) {
			e.setCancelled(true);
			if(i.getType() == InventoryType.ENCHANTING) {
				if(p.getExpToLevel() >= 112) {
					ItemStack toEnch = i.getItem(0);
					ItemMeta toEnchMeta = toEnch.getItemMeta();
					toEnchMeta.setDisplayName(main.scrollName);
					toEnch.setItemMeta(toEnchMeta);

					this.randomEnchant(toEnch);
					p.giveExpLevels(-30);
				}else { //Causes exception when not enough levels..?
					p.closeInventory();
					p.sendMessage(ChatColor.RED + "Not enough levels! (Required: 30)");
				}
			}
		}
	}

	@EventHandler(priority = EventPriority.HIGH)
	public void onInventoryClose(InventoryCloseEvent e) {
		Player p = (Player) e.getPlayer();
		Inventory pInv = p.getInventory();
		Inventory i = e.getInventory();
		if(i.equals(ew)) {
			if(scroll != null){
				pInv.addItem(scroll);
				pInv.addItem(i.getItem(ITEM_SLOT));
				i.removeItem(i.getItem(ITEM_SLOT));
			}
		}
		if(i.getType() == InventoryType.ENCHANTING) {
			if(i.getItem(1).getItemMeta().getDisplayName().equals(confirmName)) {
				i.removeItem(i.getItem(1));
			}
		}
	}

	@EventHandler(priority = EventPriority.HIGH)
	public void onInventoryOpen(InventoryOpenEvent e) {
		Player p = (Player) e.getPlayer();
		Inventory pInv = p.getInventory();
		Inventory i = e.getInventory();
		if(i.getType() == InventoryType.ENCHANTING) {
			ItemStack inHand = p.getItemInHand();
			if(inHand.getType() == Material.PAPER) {
				inHand.setAmount(inHand.getAmount() - 1);
				ItemStack paper = new ItemStack(Material.PAPER);
				i.setItem(0, paper);

				ItemStack confirmItem = new ItemStack(Material.STAINED_GLASS_PANE, 1, DyeColor.GREEN.getWoolData());
				ItemMeta confirmMeta = confirmItem.getItemMeta();
				confirmMeta.setDisplayName(confirmName);
				confirmItem.setItemMeta(confirmMeta);

				i.setItem(1, confirmItem);
			}
		}
	}

	private ItemStack randomEnchant(ItemStack toEnch) {

		List<Enchantment> enchs = new ArrayList<Enchantment>();
		for(Enchantment ench : Enchantment.values()) {
			enchs.add(ench);
		}
		Collections.shuffle(enchs);

		Random r = new Random();
		int enchNum = r.nextInt(2) + 2;
		for(int i = 0; i < enchNum; i++) {
			this.addEnchantment(toEnch, enchs.get(i), r.nextInt(4) + 1);
		}

		return toEnch;
	}

	private ItemStack addEnchantment(ItemStack item, Enchantment e, int lvl) {
		ItemMeta meta = item.getItemMeta();
		meta.addEnchant(e, lvl, true);
		item.setItemMeta(meta);
		return item;
	}

}