#fixed code
                             @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
	public void onInventoryClick(InventoryClickEvent event) {
		Inventory inventory = event.getInventory();
		if (!(inventory.getHolder() instanceof AchievementInventoryHolder) || event.getRawSlot() < 0) {
			return;
		}

		// Prevent players from taking items out of the GUI.
		event.setCancelled(true);

		// Clicking empty slots should do nothing
		if (event.getCurrentItem() == null) {
			return;
		}

		int currentPage = ((AchievementInventoryHolder) inventory.getHolder()).getPageIndex();
		Player player = (Player) event.getWhoClicked();
		if (currentPage == MAIN_GUI_PAGE) {
			// Main GUI, check whether player can interact with the selected item.
			if (event.getCurrentItem().getType() != lockedMaterial && event.getRawSlot() < getMainGUIItemCount()) {
				categoryGUI.displayCategoryGUI(event.getCurrentItem(), player, 0);
			}
			return;
		}

		ItemStack categoryItem = inventory.getItem(0);
		// Check whether a navigation button was clicked in a category GUI.
		if (isButtonClicked(event, guiItems.getBackButton())) {
			mainGUI.displayMainGUI(player);
		} else if (isButtonClicked(event, guiItems.getPreviousButton())) {
			categoryGUI.displayCategoryGUI(categoryItem, player, currentPage - 1);
		} else if (isButtonClicked(event, guiItems.getNextButton())) {
			categoryGUI.displayCategoryGUI(categoryItem, player, currentPage + 1);
		}
	}
#vulnerable code 
                             @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
	public void onInventoryClick(InventoryClickEvent event) {
		Inventory inventory = event.getInventory();
		if (!(inventory.getHolder() instanceof AchievementInventoryHolder) || event.getRawSlot() < 0) {
			return;
		}

		// Prevent players from taking items out of the GUI.
		event.setCancelled(true);

		int currentPage = ((AchievementInventoryHolder) inventory.getHolder()).getPageIndex();
		Player player = (Player) event.getWhoClicked();
		if (currentPage == MAIN_GUI_PAGE) {
			// Main GUI, check whether player can interact with the selected item.
			if (event.getCurrentItem().getType() != lockedMaterial && event.getRawSlot() < getMainGUIItemCount()) {
				categoryGUI.displayCategoryGUI(event.getCurrentItem(), player, 0);
			}
			return;
		}

		ItemStack categoryItem = inventory.getItem(0);
		// Check whether a navigation button was clicked in a category GUI.
		if (isButtonClicked(event, guiItems.getBackButton())) {
			mainGUI.displayMainGUI(player);
		} else if (isButtonClicked(event, guiItems.getPreviousButton())) {
			categoryGUI.displayCategoryGUI(categoryItem, player, currentPage - 1);
		} else if (isButtonClicked(event, guiItems.getNextButton())) {
			categoryGUI.displayCategoryGUI(categoryItem, player, currentPage + 1);
		}
	} 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE