Fixed an issue with loot chest unregistration

src/main/java/net/Indyuce/mmocore/MMOCore.java

@@ -58,7 +58,7 @@ import org.jetbrains.annotations.NotNull;
 
 import java.io.File;
 import java.lang.reflect.Field;
-import java.util.HashSet;
+import java.util.Iterator;
 import java.util.logging.Level;
 
 public class MMOCore extends LuminePlugin {
@@ -200,8 +200,14 @@ public class MMOCore extends LuminePlugin {
 		 */
 		new BukkitRunnable() {
 			public void run() {
-				for (LootChest chest : new HashSet<>(lootChests.getActive()))
-					if (chest.shouldExpire()) chest.unregister(false);
+				Iterator<LootChest> iterator = lootChests.getActive().iterator();
+				while (iterator.hasNext()) {
+					LootChest next = iterator.next();
+					if (next.shouldExpire()) {
+						iterator.remove();
+						next.expire(false);
+					}
+				}
 			}
 		}.runTaskTimer(this, 5 * 60 * 20, 5 * 60 * 20);
 
@@ -369,7 +375,7 @@ public class MMOCore extends LuminePlugin {
 		mineManager.resetRemainingBlocks();
 
 		// Clear spawned loot chests
-		lootChests.getActive().forEach(chest -> chest.unregister(false));
+		lootChests.getActive().forEach(chest -> chest.expire(false));
 	}
 
 	/**

src/main/java/net/Indyuce/mmocore/listener/LootableChestsListener.java

@@ -17,6 +17,6 @@ public class LootableChestsListener implements Listener {
 		Chest chest = (Chest) event.getInventory().getHolder();
 		LootChest lootChest = MMOCore.plugin.lootChests.getChest(chest.getLocation());
 		if (lootChest != null)
-			lootChest.unregister(true);
+			lootChest.expire(true);
 	}
 }

src/main/java/net/Indyuce/mmocore/loot/chest/LootChest.java

@@ -2,7 +2,7 @@ package net.Indyuce.mmocore.loot.chest;
 
 import net.Indyuce.mmocore.MMOCore;
 import net.Indyuce.mmocore.api.SoundEvent;
-import net.Indyuce.mmocore.manager.SoundManager;
+import org.apache.commons.lang.Validate;
 import org.bukkit.Location;
 import org.bukkit.Material;
 import org.bukkit.Particle;
@@ -12,13 +12,18 @@ import org.bukkit.block.data.BlockData;
 import org.bukkit.entity.Player;
 import org.bukkit.scheduler.BukkitRunnable;
 
+import javax.annotation.Nullable;
+
 public class LootChest {
     private final ChestTier tier;
     private final LootChestRegion region;
     private final ReplacedBlock block;
+    @Nullable
     private final BukkitRunnable effectRunnable;
     private final long date = System.currentTimeMillis();
 
+    private boolean active = true;
+
     /**
      * Called when a loot chest is placed as a Bukkit block, and used
      * to save the data of the block which has been replaced.
@@ -57,19 +62,24 @@ public class LootChest {
     }
 
     /**
+     * This does NOT remove the loot chest from the plugin registry.
+     *
      * @param player If a player triggered the unregistration of that chest by
      *               opening and then closing it for the first time. It's set
      *               to false when a loot chest expires or when MMOCore disables.
      *               <p>
      *               When no player is closing the chest, its content should be lost
      */
-    public void unregister(boolean player) {
+    public void expire(boolean player) {
+
+        // Check for expire
+        Validate.isTrue(active, "Chest has already expired");
+        active = false;
 
         // If a player is responsible of closing the chest, close it with sound
         if (player) {
             MMOCore.plugin.soundManager.getSound(SoundEvent.CLOSE_LOOT_CHEST).playAt(block.loc);
             block.loc.getWorld().spawnParticle(Particle.CRIT, block.loc.clone().add(.5, .5, .5), 16, 0, 0, 0, .5);
-            MMOCore.plugin.lootChests.unregister(this);
         }
 
         /*