From a2d2248f3bd2ea9257def07d6f6c745353d70107 Mon Sep 17 00:00:00 2001
From: Alex Peck <alexpeck@microsoft.com>
Date: Tue, 24 Oct 2023 09:29:44 -0700
Subject: [PATCH 1/2] handle null

---
 BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs | 7 +++++++
 BitFaster.Caching/Lru/ConcurrentLruCore.cs            | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs b/BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs
index ab2bdbc1..5395700e 100644
--- a/BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs
+++ b/BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs
@@ -574,6 +574,13 @@ public void WhenValueExpiresItIsDisposed()
             disposableValueFactory.Items[6].IsDisposed.Should().BeFalse();
         }
 
+        [Fact]
+        public void WhenAddingNullValueCanBeAddedAndRemoved()
+        {
+            lru.GetOrAdd(1, _ => null).Should().BeNull();
+            lru.AddOrUpdate(1, null);
+            lru.TryRemove(1).Should().BeTrue();
+        }
 
         [Fact]
         public void WhenValueEvictedItemRemovedEventIsFired()
diff --git a/BitFaster.Caching/Lru/ConcurrentLruCore.cs b/BitFaster.Caching/Lru/ConcurrentLruCore.cs
index acb3cd2e..25558fa1 100644
--- a/BitFaster.Caching/Lru/ConcurrentLruCore.cs
+++ b/BitFaster.Caching/Lru/ConcurrentLruCore.cs
@@ -359,7 +359,7 @@ private void OnRemove(K key, I item)
             this.telemetryPolicy.OnItemRemoved(key, item.Value, ItemRemovedReason.Removed);
 
             // serialize dispose (common case dispose not thread safe)
-            lock (item.Value)
+            lock (item)
             {
                 Disposer<V>.Dispose(item.Value);
             }

From 5700be01dc1dd955848ced2e5bc0f37d0c5ef959 Mon Sep 17 00:00:00 2001
From: Alex Peck <alexpeck@microsoft.com>
Date: Tue, 24 Oct 2023 11:25:41 -0700
Subject: [PATCH 2/2] lfu test

---
 BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuTests.cs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuTests.cs b/BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuTests.cs
index 796f6e74..b5d5f4a9 100644
--- a/BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuTests.cs
+++ b/BitFaster.Caching.UnitTests/Lfu/ConcurrentLfuTests.cs
@@ -672,6 +672,16 @@ public void WhenRemovedInWriteBuffer()
         public void WhenItemDoesNotExistTryUpdateIsFalse()
         {
             cache.TryUpdate(1, 2).Should().BeFalse();
+        }
+
+        [Fact]
+        public void WhenAddingNullValueCanBeAddedAndRemoved()
+        {
+            // use foreground so that any null ref exceptions will surface
+            var lfu = new ConcurrentLfu<int, string>(1, 20, new ForegroundScheduler(), EqualityComparer<int>.Default);
+            lfu.GetOrAdd(1, _ => null).Should().BeNull();
+            lfu.AddOrUpdate(1, null);
+            lfu.TryRemove(1).Should().BeTrue();
         }
 
         [Fact]