Added validation for stackables.

src/main/java/com/songoda/ultimatestacker/UltimateStacker.java

@@ -360,6 +360,12 @@ public class UltimateStacker extends SongodaPlugin {
 
 
     public void updateHologram(Hologramable stack) {
+        // Is this stack invalid?
+        if (!stack.isValid())
+            if (stack instanceof BlockStack)
+                blockStackManager.removeBlock(stack.getLocation());
+            else if (stack instanceof SpawnerStack)
+                spawnerStackManager.removeSpawner(stack.getLocation());
         // are holograms enabled?
         if (!stack.areHologramsEnabled() && !HologramManager.getManager().isEnabled()) return;
         // create the hologram

src/main/java/com/songoda/ultimatestacker/stackable/Hologramable.java

@@ -9,4 +9,6 @@ public interface Hologramable {
     String getHologramName();
 
     boolean areHologramsEnabled();
+
+    boolean isValid();
 }

src/main/java/com/songoda/ultimatestacker/stackable/Stackable.java

@@ -1,7 +0,0 @@
-package com.songoda.ultimatestacker.stackable;
-
-
-public interface Stackable {
-
-    int getAmount();
-}

src/main/java/com/songoda/ultimatestacker/stackable/block/BlockStack.java

@@ -4,7 +4,7 @@ import com.songoda.core.compatibility.CompatibleMaterial;
 import com.songoda.ultimatestacker.UltimateStacker;
 import com.songoda.ultimatestacker.settings.Settings;
 import com.songoda.ultimatestacker.stackable.Hologramable;
-import com.songoda.ultimatestacker.stackable.Stackable;
+import com.songoda.ultimatestacker.utils.Stackable;
 import com.songoda.ultimatestacker.utils.Methods;
 import org.bukkit.Location;
 import org.bukkit.World;
@@ -34,6 +34,11 @@ public class BlockStack implements Stackable, Hologramable {
         return amount;
     }
 
+    @Override
+    public boolean isValid() {
+        return CompatibleMaterial.getMaterial(location.getBlock()) == material;
+    }
+
     public void add(int amount) {
         this.amount = this.amount + amount;
     }

src/main/java/com/songoda/ultimatestacker/stackable/entity/ColdEntityStack.java

@@ -3,7 +3,7 @@ package com.songoda.ultimatestacker.stackable.entity;
 import com.songoda.core.nms.NmsManager;
 import com.songoda.core.nms.nbt.NBTEntity;
 import com.songoda.ultimatestacker.UltimateStacker;
-import com.songoda.ultimatestacker.stackable.Stackable;
+import com.songoda.ultimatestacker.utils.Stackable;
 import org.bukkit.Location;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.LivingEntity;
@@ -97,6 +97,11 @@ public class ColdEntityStack implements Stackable {
         return stackedEntities.size() + 1;
     }
 
+    @Override
+    public boolean isValid() {
+        return true;
+    }
+
     public void createDuplicates(int duplicates) {
         this.createDuplicates = duplicates;
     }

src/main/java/com/songoda/ultimatestacker/stackable/spawner/SpawnerStack.java

@@ -1,10 +1,11 @@
 package com.songoda.ultimatestacker.stackable.spawner;
 
+import com.songoda.core.compatibility.CompatibleMaterial;
 import com.songoda.core.compatibility.ServerVersion;
 import com.songoda.ultimatestacker.UltimateStacker;
 import com.songoda.ultimatestacker.settings.Settings;
 import com.songoda.ultimatestacker.stackable.Hologramable;
-import com.songoda.ultimatestacker.stackable.Stackable;
+import com.songoda.ultimatestacker.utils.Stackable;
 import com.songoda.ultimatestacker.utils.Methods;
 import com.songoda.ultimatestacker.utils.Reflection;
 import org.bukkit.Bukkit;
@@ -34,6 +35,11 @@ public class SpawnerStack implements Stackable, Hologramable {
         return amount;
     }
 
+    @Override
+    public boolean isValid() {
+        return CompatibleMaterial.getMaterial(location.getBlock()) == CompatibleMaterial.SPAWNER;
+    }
+
     public void setAmount(int amount) {
         this.amount = amount;
         plugin.getDataManager().updateSpawner(this);

src/main/java/com/songoda/ultimatestacker/utils/Stackable.java

@@ -0,0 +1,9 @@
+package com.songoda.ultimatestacker.utils;
+
+
+public interface Stackable {
+
+    int getAmount();
+
+    boolean isValid();
+}