NullPointerException

I'm sure that I'm a newb, and it's really obvious, but I don't code in Java much. I looked around, and messed with the code a lot, but to no avail, so I came here.
Caused by: java.lang.NullPointerException
at org.bukkit.inventory.ItemStack.<init>(ItemStack.java:57)
at cc.co.ghostsailor.CopyBook.CopyBook.chestCreate(CopyBook.java:134)
at cc.co.ghostsailor.CopyBook.CopyBook.onCommand(CopyBook.java:112)
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
... 15 more

Sorry if my code is a mess. I try to keep it organized, but it gets out of control sometimes.
My source is

Code:java

package cc.co.ghostsailor.CopyBook;
 
import java.util.*;
import java.util.logging.Logger;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.block.Chest;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.PlayerInventory;
import org.bukkit.permissions.Permission;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.command.*;
 
public class CopyBook extends JavaPlugin
    implements CommandExecutor
    {
 
        public CopyBook()
        {
        }
 
        public void onEnable()
        {
            log = getLogger();
            log.info("CopyBook online.");
        }
 
        public void onDisable()
        {
            log.info("CopyBook offline.");
        }
 
        public boolean onCommand(CommandSender cs, Command command, String arg2, String cmd[])
        {
            if(command.getName().equalsIgnoreCase("copybook") || command.getName().equalsIgnoreCase("cb"))
            {
                Player player;
                if(cs instanceof Player)
                {
                    player = (Player)cs;
                } else
                {
                    cs.sendMessage("You must run this command as a player, as it relies on the item you have in your hand.");
                    return false;
                }
                if (player.hasPermission("CopyBook")) {
                    PlayerInventory inv = player.getInventory();
                    int slot = inv.getHeldItemSlot();
                    ItemStack book = inv.getItem(slot);
                    if(!book.getType().equals(Material.BOOK_AND_QUILL) && !book.getType().equals(Material.WRITTEN_BOOK))
                    {
                        cs.sendMessage("Please hold the book and quill or written book that you wish to copy and try again.");
                        return false;
                    }
                    int ti = -1;
                    ItemStack ts = null;
                    Map tss = inv.all(Material.INK_SACK);
                    for(Iterator iterator = tss.entrySet().iterator(); iterator.hasNext();)
                    {
                        java.util.Map.Entry entry = (java.util.Map.Entry)iterator.next();
                        ti = ((Integer)entry.getKey()).intValue();
                        ts = (ItemStack)entry.getValue();
                        if(ts.getData().getData() == 0)
                            break;
                    }
 
                    if(ts == null || ts.getData().getData() != 0)
                    {
                        cs.sendMessage("You do not have enough ink sacs.");
                        return false;
                    }
                    if(!inv.contains(Material.BOOK))
                    {
                        cs.sendMessage("You do not have enough books.");
                        return false;
                    }
                    if(!inv.contains(Material.FEATHER))
                    {
                        cs.sendMessage("You do not have enough feathers.");
                        return false;
                    }
                    if(ts.getAmount() == 1)
                        inv.setItem(ti, new ItemStack(Material.AIR));
                    else
                        ts.setAmount(ts.getAmount() - 1);
                    ti = inv.first(Material.BOOK);
                    ts = inv.getItem(ti);
                    if(ts.getAmount() == 1)
                        inv.setItem(ti, new ItemStack(Material.AIR));
                    else
                        ts.setAmount(ts.getAmount() - 1);
                    ti = inv.first(Material.FEATHER);
                    ts = inv.getItem(ti);
                    if(ts.getAmount() == 1)
                        inv.setItem(ti, new ItemStack(Material.AIR));
                    else
                        ts.setAmount(ts.getAmount() - 1);
                    //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\
                    Block lookingBlock = ((Player)cs).getTargetBlock(null, 0);
                    Block targetBlock;
                    if(lookingBlock.getType() == Material.SNOW)
                        targetBlock = lookingBlock;
                    else
                        targetBlock = lookingBlock.getRelative(0, 1, 0);
                    if(targetBlock.getType() != Material.AIR && targetBlock.getType() != Material.SNOW)
                    {
                        cs.sendMessage((new StringBuilder(String.valueOf(prefix))).append("Could not copy, the block above target is not air.").toString());
                        return true;
                    }
                    if(targetBlock==null){return false;}else{
                        if(chestCreate(cs, targetBlock))
                        {
                            return true;
                        }
                    }
                }
                    return true;
                } else
                {
                    return false;
                }
        }
        private boolean chestCreate(CommandSender cs, Block targetBlock)
        {
            Material mat = null;
            Byte bdata = null;
            Player player;
            player = (Player)cs;
            PlayerInventory inv = player.getInventory();
            int slot = inv.getHeldItemSlot();
            ItemStack book = inv.getItem(slot);
            if(book == null){return false;} else {
            ItemStack iStack = new ItemStack(mat, 1, (short)0, bdata);   
            targetBlock.setTypeId(54);
            Chest chest = (Chest)targetBlock.getState();
            for(int i = 0; i <= 26; i++)
                chest.getInventory().addItem(new ItemStack[] {
                    book.clone()
                });
 
            cs.sendMessage((new StringBuilder(String.valueOf(prefix))).append("Created a full chest of \2477").append(mat.toString()).append("\247f for you!").toString());
            return true;
            }
        }
    Logger log;
    public CopyBook fc;
    String prefix;
    Permission copybook;
    Permission reload;
}

 

What is on line:

at cc.co.ghostsailor.CopyBook.CopyBook.chestCreate(CopyBook.java:134) <---- line 134
at cc.co.ghostsailor.CopyBook.CopyBook.onCommand(CopyBook.java:112) <---- line 112

 

Line 134 is ItemStack iStack = new ItemStack(mat, 1, (short)0, bdata);
Line 112 is calling it, if(chestCreate(cs, targetBlock))

 

Line 134: ItemStack iStack =new ItemStack(mat, 1, (short)0, bdata);

Line 112: if(chestCreate(cs, targetBlock))

 

both, mat and bdata are null:
Material mat = null;
Byte bdata = null;

 

Oh, okay. I knew it was going to be totally obvious and I'd miss it.
Thanks.