API improvements.

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

@@ -16,6 +16,7 @@ import org.bukkit.inventory.ItemStack;
 import org.bukkit.util.Vector;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.ThreadLocalRandom;
 
@@ -41,6 +42,20 @@ public class EntityStack extends ColdEntityStack {
         return stackedEntity;
     }
 
+    @Override
+    public List<StackedEntity> takeEntities(int amount) {
+        List<StackedEntity> entities = super.takeEntities(amount);
+        if (this.stackedEntities.isEmpty())
+            destroy(true);
+        return entities;
+    }
+
+    @Override
+    public List<StackedEntity> takeAllEntities() {
+        destroy(true);
+        return super.takeAllEntities();
+    }
+
     public void updateStack() {
         if (createDuplicates != 0) {
             List<StackedEntity> stackedEntities = new ArrayList<>();

src/main/java/com/songoda/ultimatestacker/tasks/StackingTask.java

@@ -189,16 +189,16 @@ public class StackingTask extends BukkitRunnable {
 
                 // If we are a stack lets merge our stack with the just found friend stack.
                 if (isStack) {
+                    // Get the host entity.
+                    StackedEntity host = stack.getHostAsStackedEntity();
                     // Get all the stacked entities in our stack and add them to a list.
                     List<StackedEntity> entities = stack.takeAllEntities();
                     // Add the host to this list.
-                    entities.add(stack.getHostAsStackedEntity());
+                    entities.add(host);
                     // Add the collected entities to the new stack.
                     friendStack.addEntitiesToStackSilently(entities);
                     // Update friend stack to display changes.
                     friendStack.updateStack();
-                    // Destroy our stack.
-                    stack.destroy();
                     // Push changes to the database.
                     plugin.getDataManager().createStackedEntities(friendStack, entities);
                 } else {