java.lang.ArrayIndexOutOfBoundsException: 0 HELP! Please!

HELP! I'm getting this error on my plugin:

Code:

Caused by:  java.lang.ArrayIndexOutOfBoundsException: 0
   at me.mrcreeper242.Ticket.onCommand<Ticket.java:41>~[?:?]
at org.bukkit.command.PluginCommand.execute<PluginCommand.java:44> ~[serve.jar:git-Spigot-1649]

Here is my plugin code:

Code:

package me.mrcreeper242;

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

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.metadata.FixedMetadataValue;
import org.bukkit.metadata.MetadataValue;
import org.bukkit.plugin.Plugin;
import org.bukkit.plugin.java.JavaPlugin;

public class Ticket extends JavaPlugin{

    private List<Player> cantDoCommand = new ArrayList<Player>();
   
    private final String KEY = "Ticket";
   
    CountDown d = new CountDown();
   
    @Override
    public void onEnable() {
       
    }
       
    @Override
    public void onDisable() {
       
    }
   
   
   
      public boolean onCommand(CommandSender sender, Command cmd, String commandLabel, String[] args){
          Player p = (Player) sender;
          Player s = Bukkit.getPlayer(args[0]);
          ItemStack item = p.getItemInHand();
          ItemMeta meta = item.getItemMeta();
               ItemStack i = new ItemStack(Material.PAPER, 1);
              ItemMeta itemMeta = i.getItemMeta();
              itemMeta.setDisplayName(ChatColor.BLUE + "Ticket");
              i.setItemMeta(itemMeta);
              if(commandLabel.equalsIgnoreCase("Ticket")) {
                  if(p.hasPermission("ticket.use")) {
             

             
              if((sender instanceof Player)) {
                  if(!cantDoCommand.contains(p)) {
                      p.getInventory().addItem(new ItemStack(i));
                      cantDoCommand.add(p);
                      d.setList(cantDoCommand);
                      d.setPlayer(p);
                      p.sendMessage(ChatColor.GREEN + "Here is your ticket!");
                      new Thread(d).start();
                  } else if(cantDoCommand.contains(p)) {
                      p.sendMessage(ChatColor.RED + "You can only use this command once every two days.");
                  }
              }
             
                  } else if(!p.hasPermission("ticket.use")) {
                      p.sendMessage("You need a donator rank to claim a ticket!");
                  }
         
          } else if(commandLabel.equalsIgnoreCase("TicketRegister")) {
              if(p.getInventory().contains(Material.PAPER)) {
              if(item.hasItemMeta()){
                  if(meta.getDisplayName().contains((ChatColor.stripColor((ChatColor.BLUE + "Ticket"))))){
                      p.sendMessage(ChatColor.GREEN + "Registered!");
                      p.getInventory().removeItem(new ItemStack(Material.PAPER));
                      setMetadata(p, KEY, p, this);
                 
              }
          } else if(!item.hasItemMeta()) {
              p.sendMessage(ChatColor.RED + "You need a ticket to register!");
          }
             
          }
             
          } else if(commandLabel.equalsIgnoreCase("TicketCheck")) {
              if(p.hasPermission("ticket.check")) {
              if(args.length == 1) {
              if(hasMetadata(s, KEY, this)) {
                  p.sendMessage(ChatColor.GREEN + "Player has registered a ticket!");
                  p.removeMetadata(KEY, this);
              } else if(!hasMetadata(s, KEY, this)) {
                  p.sendMessage(ChatColor.RED+"Player has not registered a ticket!");

              }
             
          } else {
              p.sendMessage(ChatColor.RED + "Usage:");
              p.sendMessage(ChatColor.RED + "/ticketcheck <Player Name>");
          }
             
          } else {
              p.sendMessage(ChatColor.RED + "You do not have permission");
          }
             
          }
            
             
          
            return true;
        }
     
     
      class CountDown implements Runnable {
         
          public Player player = null;
          public List<Player> cantDoCommand = new ArrayList<Player>();
         
         
          public void setPlayer(Player player) {
              this.player = player;
          }
         
          public void setList(List<Player> list) {
              cantDoCommand = list;
          }
         
          public List<Player> getList() {
              return cantDoCommand;
          }

        public void run() {
            try {
                Thread.sleep(5000);
                cantDoCommand.remove(player);
               
            }catch(Exception ingored) {
               
            }
           
        }
         
      }
     
      public void setMetadata(Player player, String key, Player value, Plugin plugin) {
          player.setMetadata(key, new FixedMetadataValue(plugin, value));
      }
     
      public Player getMetadata(Player player, String key, Plugin plugin) {
          List<MetadataValue> values = player.getMetadata(key);
          for(MetadataValue val: values) {
              if(val.getOwningPlugin().getDescription().getName().equals(plugin.getDescription().getName())) {
                  return (Player) val.value();
              }
          }
         
         
          return null;
      }
     
      public boolean hasMetadata(Player player, String key, Plugin plugin) {
          List<MetadataValue> values = player.getMetadata(key);
          for(MetadataValue val: values) {
              if(val.getOwningPlugin().getDescription().getName().equals(plugin.getDescription().getName())) {
                  return true;
              }
          }
         
         
          return false;
         
      }
     
}

 

Look, argument [0] is the first argument you pass in. But your code does not check how many arguments are being passed in. So if you ran /ticket, and didn't give an argument, well. You get errors. Write your code properly, check for argument count, check if argument[0] is even a player, check if that player is online, etc. Also add those checks IN ORDER, so first do /ticket, then check argument count, then check if argument 0 is player, then act upon that player accordingly