Material is null

I am currently Stuck on Material cannot be Null. I am currently Developing a SignShop Plugin. I am Learning this type of stuff.

Code:

package main;

import net.milkbowl.vault.economy.Economy;
import net.milkbowl.vault.economy.EconomyResponse;
import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.Server;
import org.bukkit.block.Block;
import org.bukkit.block.Sign;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.entity.Player;
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.player.PlayerInteractEvent;
import org.bukkit.inventory.ItemStack;
import me.idlibrary.main.IDLibrary;

public class SignUse
  implements Listener
{
    @EventHandler
  public void SignClick(PlayerInteractEvent event) {
    Player p = event.getPlayer();
    if (event.getAction() == Action.RIGHT_CLICK_BLOCK) {
        if (event.getClickedBlock().getState() instanceof Sign) {
            Sign sign = (Sign) event.getClickedBlock().getState();
           
            String line1 = sign.getLine(1);
            String[] splited1 = line1.split("(?<=\\D)(?=\\d)");
            //int number = Integer.valueOf(splited1[1]);
           
           

           
            if (sign.getLine(0).equalsIgnoreCase(ChatColor.BLUE + "[Admin]")) {
                //p.sendMessage(splited1[1]);
                int cost = Integer.valueOf(splited1[1]);
                  if (sign.getLine(1).contains("B $" +cost)) {
                      p.sendMessage(String.valueOf(cost));
                      p.sendMessage("RightClicked");
                     
                     
                        int amount = Integer.valueOf(sign.getLine(2));
                        //String isu = sign.getLine(1).replace("$", "");
                        //double i = Double.parseDouble(isu);
                       
                        EconomyResponse r = main.r.econ.withdrawPlayer(p.getName(), cost);
                        if (r.transactionSuccess())
                        {
                          p.sendMessage(ChatColor.GREEN + main.c.getString("TXT1") + " " + ChatColor.GOLD + "$"+cost);
                         
                          //String IDData = IDLibrary.getIDData(Material.valueOf(sign.getLine(3)));
                          //String.valueOf(sign.getLine(3))
                         // This part 
                          Material M = IDLibrary.getMaterial(String.valueOf(sign.getLine(3)));
                          ItemStack item = new ItemStack(M, amount);
                          p.getInventory().addItem(item);

                        }
                        else
                        {
                          p.sendMessage(ChatColor.RED + main.c.getString("TXT2"));
                        }
                                         
                      }                     
                  }   
            }       
        }   
    }
  }