diff --git a/Projects/UOContent/Items/Containers/TreasureMapChest.cs b/Projects/UOContent/Items/Containers/TreasureMapChest.cs
index 03e7922ee..5b3153892 100644
--- a/Projects/UOContent/Items/Containers/TreasureMapChest.cs
+++ b/Projects/UOContent/Items/Containers/TreasureMapChest.cs
@@ -361,12 +361,12 @@ public partial class TreasureMapChest : LockableContainer
 
     public override void OnItemLifted(Mobile from, Item item)
     {
-        var notYetLifted = !_lifted.Contains(item);
-
+        var notYetLifted = _lifted?.Contains(item) != true; 
         from.RevealingAction();
 
         if (notYetLifted)
         {
+            _lifted ??= new HashSet<Item>();
             _lifted.Add(item);
 
             if (Utility.RandomDouble() <= 0.1) // 10% chance to spawn a new monster