Concurrency update

src/engine/objects/NPC.java

@@ -35,6 +35,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import static engine.net.client.msg.ErrorPopupMsg.sendErrorPopup;
@@ -872,7 +873,7 @@ public class NPC extends AbstractCharacter {
         // If NPC is a vendor then configure ForgeManager support
 
         if (this.contract.isTrainer() == false)
-            ForgeManager.vendorWorkOrderLookup.computeIfAbsent(this, k -> new ArrayList<>());
+            ForgeManager.vendorWorkOrderLookup.computeIfAbsent(this, k -> new CopyOnWriteArrayList<>());
 
         this.symbol = this.contract.getIconID();
         this.modTypeTable = this.contract.getNPCModTypeTable();