Code modifié

private final String nomShop = "Le nom";

   @EventHandler
   public void onClick(InventoryClickEvent e){
       InventoryView invview = e.getView();
       Player p = (Player) e.getWhoClicked();
       if(e.getCurrentItem() == null){
           return;
       }
       if(invview.getTitle().equals(nomShop)){
           e.setCancelled(true);
           if(e.getCurrentItem().getType() == Material.DIRT){
               p.closeInventory();
               p.setGameMode(GameMode.SPECTATOR);
           }
       }
   }
   @Override
   public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args){
       if(cmd.getName().equalsIgnoreCase("shop")){
           if(!(sender instanceof Player)){
           return false;
       }
       Player p = (Player) sender;
       Inventory inv = Bukkit.createInventory(null, 9, nomShop);
       ItemStack dirt = new ItemStack(Material.DIRT);
       ItemMeta dirtMeta = dirt.getItemMeta();
       dirtMeta.setDisplayName("Item");
       dirt.setItemMeta(dirtMeta);
       inv.setItem(4, dirt);
       p.openInventory(inv);
       }
       return false;
   }