Java firework plugin

package me.DJsZ.DJsZ;



import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.block.Dispenser;
import org.bukkit.block.Sign;
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.BlockDispenseEvent;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;

public class DJsZ extends JavaPlugin implements Listener {
    @Override
    public void onEnable(){
        getLogger().info("DJsZ has been succesfull enabled!");
        this.getServer().getPluginManager().registerEvents(this, this);
    }
    @Override
    public void onDisable() {
        getLogger().info("DJsZ has been succesfull Disabled!");
    }
    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    public void onDispense(BlockDispenseEvent event){
        ItemStack dispenses = event.getItem();
        Bukkit.getServer().broadcastMessage(event.getItem().getType().name());
        if (dispenses.getType().equals(Material.FIREWORK)){
            Block block = event.getBlock();
            Block blockRel = block.getRelative(BlockFace.SOUTH, 1);
            Block blockNORTH = block.getRelative(BlockFace.NORTH, 1);
            Block blockWEST = block.getRelative(BlockFace.WEST, 1);
            Block blockEAST = block.getRelative(BlockFace.EAST, 1);
            if (blockRel.getType() == Material.WALL_SIGN) {
                Inventory inv = ((Dispenser)event.getBlock().getState()).getInventory();
                if (!inv.contains(dispenses.getType())){
                    inv.clear();
                }

                dispenses.setAmount(64);
                inv.addItem(dispenses);
                Bukkit.getServer().broadcastMessage("Hoi");
            }
        }

    }

    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    public void onBlockPlace(BlockPlaceEvent event) {
        Block block = event.getBlockPlaced();
        Block blockRel = block.getRelative(BlockFace.NORTH, 1);
        Player player = (Player) event.getPlayer();
        if (block.getType() == Material.WALL_SIGN) {
            if (blockRel.getType() == Material.DISPENSER) {
                player.sendMessage("Infinite Firework created!");
                Sign sign = (Sign) block.getState();
                sign.setLine(0,"test"); // This part isn't working
            }
        }
    }

}