Fix the hopper protection

src/main/java/com/Acrobot/Breeze/Utils/BlockUtil.java

@@ -1,12 +1,12 @@
 package com.Acrobot.Breeze.Utils;
 
-import org.bukkit.block.Block;
+import org.bukkit.block.*;
 import org.bukkit.block.Chest;
 import org.bukkit.block.Sign;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.InventoryHolder;
-import org.bukkit.material.Attachable;
+import org.bukkit.material.*;
 
 /**
  * @author Acrobot
@@ -32,6 +32,16 @@ public class BlockUtil {
         return block.getState() instanceof Chest;
     }
 
+    /**
+     * Checks if the InventoryHolder is a chest
+     *
+     * @param holder Inventory holder to check
+     * @return Is this holder a chest?
+     */
+    public static boolean isChest(InventoryHolder holder) {
+        return holder instanceof Chest || holder instanceof DoubleChest;
+    }
+
     /**
      * Gets the block to which the sign is attached
      *

src/main/java/com/Acrobot/ChestShop/Listeners/Item/ItemMoveListener.java

@@ -1,5 +1,6 @@
 package com.Acrobot.ChestShop.Listeners.Item;
 
+import com.Acrobot.Breeze.Utils.BlockUtil;
 import com.Acrobot.ChestShop.Signs.ChestShopSign;
 import org.bukkit.block.BlockState;
 import org.bukkit.block.Chest;
@@ -14,11 +15,11 @@ public class ItemMoveListener implements Listener {
 
     @EventHandler
     public static void onItemMove(InventoryMoveItemEvent event) {
-        if (event.getSource() == null || !(event.getSource().getHolder() instanceof Chest)) {
+        if (event.getSource() == null || !BlockUtil.isChest(event.getSource().getHolder())) {
             return;
         }
 
-        if (!ChestShopSign.isShopChest(((BlockState) event.getSource().getHolder()).getBlock())) {
+        if (!ChestShopSign.isShopChest(event.getSource().getHolder())) {
             return;
         }
 

src/main/java/com/Acrobot/ChestShop/Signs/ChestShopSign.java

@@ -7,9 +7,11 @@ import com.Acrobot.ChestShop.Utils.uBlock;
 import com.Acrobot.ChestShop.Utils.uName;
 import org.bukkit.block.Block;
 import org.bukkit.block.Chest;
+import org.bukkit.block.DoubleChest;
 import org.bukkit.block.Sign;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryHolder;
 
 import java.util.regex.Pattern;
 
@@ -61,6 +63,20 @@ public class ChestShopSign {
         return uBlock.getConnectedSign((Chest) chest.getState()) != null;
     }
 
+    public static boolean isShopChest(InventoryHolder holder) {
+        if (!BlockUtil.isChest(holder)) {
+            return false;
+        }
+
+        if (holder instanceof DoubleChest) {
+            return isShopChest(((DoubleChest) holder).getLocation().getBlock());
+        } else if (holder instanceof Chest) {
+            return isShopChest(((Chest) holder).getBlock());
+        } else {
+            return false;
+        }
+    }
+
     public static boolean canAccess(Player player, Sign sign) {
         if (player == null) return false;
         if (sign == null) return true;