Fix TNTSimulatorListener

Signed-off-by: yoyosource <yoyosource@nidido.de>

BauSystem_Main/src/de/steamwar/bausystem/features/simulator/TNTSimulatorListener.java

@@ -104,7 +104,8 @@ public class TNTSimulatorListener implements Listener {
 
     private void simulatorShowHide(Player player, Function<PlayerInventory, ItemStack> itemStackFunction, Location location) {
         TNTSimulator simulator = get(player);
-        if (!itemStackFunction.apply(player.getInventory()).isSimilar(WAND)) {
+        ItemStack itemStack = itemStackFunction.apply(player.getInventory());
+        if (itemStack == null || !itemStack.isSimilar(WAND)) {
             simulator.hide();
             return;
         }