diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.cs
index 055c97089a7ca..3476a93dcf6a4 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.cs
@@ -21,8 +21,8 @@ public DistributedCacheEntryOptions() { }
     }
     public static partial class DistributedCacheExtensions
     {
-        public static string GetString(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key) { throw null; }
-        public static System.Threading.Tasks.Task<string> GetStringAsync(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key, System.Threading.CancellationToken token = default(System.Threading.CancellationToken)) { throw null; }
+        public static string? GetString(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key) { throw null; }
+        public static System.Threading.Tasks.Task<string?> GetStringAsync(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key, System.Threading.CancellationToken token = default(System.Threading.CancellationToken)) { throw null; }
         public static void Set(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key, byte[] value) { }
         public static System.Threading.Tasks.Task SetAsync(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key, byte[] value, System.Threading.CancellationToken token = default(System.Threading.CancellationToken)) { throw null; }
         public static void SetString(this Microsoft.Extensions.Caching.Distributed.IDistributedCache cache, string key, string value) { }
@@ -32,8 +32,8 @@ public static void SetString(this Microsoft.Extensions.Caching.Distributed.IDist
     }
     public partial interface IDistributedCache
     {
-        byte[] Get(string key);
-        System.Threading.Tasks.Task<byte[]> GetAsync(string key, System.Threading.CancellationToken token = default(System.Threading.CancellationToken));
+        byte[]? Get(string key);
+        System.Threading.Tasks.Task<byte[]?> GetAsync(string key, System.Threading.CancellationToken token = default(System.Threading.CancellationToken));
         void Refresh(string key);
         System.Threading.Tasks.Task RefreshAsync(string key, System.Threading.CancellationToken token = default(System.Threading.CancellationToken));
         void Remove(string key);
@@ -48,7 +48,7 @@ public static partial class CacheEntryExtensions
     {
         public static Microsoft.Extensions.Caching.Memory.ICacheEntry AddExpirationToken(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, Microsoft.Extensions.Primitives.IChangeToken expirationToken) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.ICacheEntry RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback) { throw null; }
-        public static Microsoft.Extensions.Caching.Memory.ICacheEntry RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback, object state) { throw null; }
+        public static Microsoft.Extensions.Caching.Memory.ICacheEntry RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback, object? state) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.ICacheEntry SetAbsoluteExpiration(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, System.DateTimeOffset absolute) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.ICacheEntry SetAbsoluteExpiration(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, System.TimeSpan relative) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.ICacheEntry SetOptions(this Microsoft.Extensions.Caching.Memory.ICacheEntry entry, Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options) { throw null; }
@@ -59,16 +59,16 @@ public static partial class CacheEntryExtensions
     }
     public static partial class CacheExtensions
     {
-        public static object Get(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key) { throw null; }
-        public static System.Threading.Tasks.Task<TItem> GetOrCreateAsync<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, System.Func<Microsoft.Extensions.Caching.Memory.ICacheEntry, System.Threading.Tasks.Task<TItem>> factory) { throw null; }
-        public static TItem GetOrCreate<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, System.Func<Microsoft.Extensions.Caching.Memory.ICacheEntry, TItem> factory) { throw null; }
-        public static TItem Get<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key) { throw null; }
-        public static TItem Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem value) { throw null; }
-        public static TItem Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem value, Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options) { throw null; }
-        public static TItem Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem value, Microsoft.Extensions.Primitives.IChangeToken expirationToken) { throw null; }
-        public static TItem Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem value, System.DateTimeOffset absoluteExpiration) { throw null; }
-        public static TItem Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem value, System.TimeSpan absoluteExpirationRelativeToNow) { throw null; }
-        public static bool TryGetValue<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, out TItem value) { throw null; }
+        public static object? Get(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key) { throw null; }
+        public static System.Threading.Tasks.Task<TItem> GetOrCreateAsync<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, System.Func<Microsoft.Extensions.Caching.Memory.ICacheEntry, System.Threading.Tasks.Task<TItem?>> factory) { throw null; }
+        public static TItem? GetOrCreate<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, System.Func<Microsoft.Extensions.Caching.Memory.ICacheEntry, TItem?> factory) { throw null; }
+        public static TItem? Get<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key) { throw null; }
+        public static TItem? Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem? value) { throw null; }
+        public static TItem? Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem? value, Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions? options) { throw null; }
+        public static TItem? Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem? value, Microsoft.Extensions.Primitives.IChangeToken expirationToken) { throw null; }
+        public static TItem? Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem? value, System.DateTimeOffset absoluteExpiration) { throw null; }
+        public static TItem? Set<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, TItem? value, System.TimeSpan absoluteExpirationRelativeToNow) { throw null; }
+        public static bool TryGetValue<TItem>(this Microsoft.Extensions.Caching.Memory.IMemoryCache cache, object key, out TItem? value) { throw null; }
     }
     public enum CacheItemPriority
     {
@@ -96,19 +96,19 @@ public partial interface ICacheEntry : System.IDisposable
         Microsoft.Extensions.Caching.Memory.CacheItemPriority Priority { get; set; }
         long? Size { get; set; }
         System.TimeSpan? SlidingExpiration { get; set; }
-        object Value { get; set; }
+        object? Value { get; set; }
     }
     public partial interface IMemoryCache : System.IDisposable
     {
         Microsoft.Extensions.Caching.Memory.ICacheEntry CreateEntry(object key);
         void Remove(object key);
-        bool TryGetValue(object key, out object value);
+        bool TryGetValue(object key, out object? value);
     }
     public static partial class MemoryCacheEntryExtensions
     {
         public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions AddExpirationToken(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, Microsoft.Extensions.Primitives.IChangeToken expirationToken) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback) { throw null; }
-        public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback, object state) { throw null; }
+        public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions RegisterPostEvictionCallback(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, Microsoft.Extensions.Caching.Memory.PostEvictionDelegate callback, object? state) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions SetAbsoluteExpiration(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, System.DateTimeOffset absolute) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions SetAbsoluteExpiration(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, System.TimeSpan relative) { throw null; }
         public static Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions SetPriority(this Microsoft.Extensions.Caching.Memory.MemoryCacheEntryOptions options, Microsoft.Extensions.Caching.Memory.CacheItemPriority priority) { throw null; }
@@ -129,10 +129,10 @@ public MemoryCacheEntryOptions() { }
     public partial class PostEvictionCallbackRegistration
     {
         public PostEvictionCallbackRegistration() { }
-        public Microsoft.Extensions.Caching.Memory.PostEvictionDelegate EvictionCallback { get { throw null; } set { } }
-        public object State { get { throw null; } set { } }
+        public Microsoft.Extensions.Caching.Memory.PostEvictionDelegate? EvictionCallback { get { throw null; } set { } }
+        public object? State { get { throw null; } set { } }
     }
-    public delegate void PostEvictionDelegate(object key, object value, Microsoft.Extensions.Caching.Memory.EvictionReason reason, object state);
+    public delegate void PostEvictionDelegate(object key, object? value, Microsoft.Extensions.Caching.Memory.EvictionReason reason, object? state);
 }
 namespace Microsoft.Extensions.Internal
 {
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
index 8895a198c5c3e..9d967d4f3adb2 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/CacheEntryExtensions.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/CacheEntryExtensions.cs
index 1adf580d2b714..ab8305044ea9e 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/CacheEntryExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/CacheEntryExtensions.cs
@@ -112,7 +112,7 @@ public static ICacheEntry RegisterPostEvictionCallback(
         public static ICacheEntry RegisterPostEvictionCallback(
             this ICacheEntry entry,
             PostEvictionDelegate callback,
-            object state)
+            object? state)
         {
             if (callback == null)
             {
@@ -186,7 +186,7 @@ public static ICacheEntry SetOptions(this ICacheEntry entry, MemoryCacheEntryOpt
 
             foreach (PostEvictionCallbackRegistration postEvictionCallback in options.PostEvictionCallbacks)
             {
-                entry.RegisterPostEvictionCallback(postEvictionCallback.EvictionCallback, postEvictionCallback.State);
+                entry.RegisterPostEvictionCallback(postEvictionCallback.EvictionCallback!, postEvictionCallback.State);
             }
 
             return entry;
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/DistributedCacheExtensions.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/DistributedCacheExtensions.cs
index 621321ce975d3..562d8e224c075 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/DistributedCacheExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/DistributedCacheExtensions.cs
@@ -133,9 +133,9 @@ public static void SetString(this IDistributedCache cache, string key, string va
         /// <param name="cache">The cache in which to store the data.</param>
         /// <param name="key">The key to get the stored data for.</param>
         /// <returns>The string value from the stored cache key.</returns>
-        public static string GetString(this IDistributedCache cache, string key)
+        public static string? GetString(this IDistributedCache cache, string key)
         {
-            byte[] data = cache.Get(key);
+            byte[]? data = cache.Get(key);
             if (data == null)
             {
                 return null;
@@ -150,9 +150,9 @@ public static string GetString(this IDistributedCache cache, string key)
         /// <param name="key">The key to get the stored data for.</param>
         /// <param name="token">Optional. A <see cref="CancellationToken" /> to cancel the operation.</param>
         /// <returns>A task that gets the string value from the stored cache key.</returns>
-        public static async Task<string> GetStringAsync(this IDistributedCache cache, string key, CancellationToken token = default(CancellationToken))
+        public static async Task<string?> GetStringAsync(this IDistributedCache cache, string key, CancellationToken token = default(CancellationToken))
         {
-            byte[] data = await cache.GetAsync(key, token).ConfigureAwait(false);
+            byte[]? data = await cache.GetAsync(key, token).ConfigureAwait(false);
             if (data == null)
             {
                 return null;
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/ICacheEntry.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/ICacheEntry.cs
index be1cf5ccc0d35..02ff52ee5942a 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/ICacheEntry.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/ICacheEntry.cs
@@ -20,7 +20,7 @@ public interface ICacheEntry : IDisposable
         /// <summary>
         /// Gets or set the value of the cache entry.
         /// </summary>
-        object Value { get; set; }
+        object? Value { get; set; }
 
         /// <summary>
         /// Gets or sets an absolute expiration date for the cache entry.
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IDistributedCache.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IDistributedCache.cs
index d3b32ec54c03e..7be960251823b 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IDistributedCache.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IDistributedCache.cs
@@ -16,7 +16,7 @@ public interface IDistributedCache
         /// </summary>
         /// <param name="key">A string identifying the requested value.</param>
         /// <returns>The located value or null.</returns>
-        byte[] Get(string key);
+        byte[]? Get(string key);
 
         /// <summary>
         /// Gets a value with the given key.
@@ -24,7 +24,7 @@ public interface IDistributedCache
         /// <param name="key">A string identifying the requested value.</param>
         /// <param name="token">Optional. The <see cref="CancellationToken"/> used to propagate notifications that the operation should be canceled.</param>
         /// <returns>The <see cref="Task"/> that represents the asynchronous operation, containing the located value or null.</returns>
-        Task<byte[]> GetAsync(string key, CancellationToken token = default(CancellationToken));
+        Task<byte[]?> GetAsync(string key, CancellationToken token = default(CancellationToken));
 
         /// <summary>
         /// Sets a value with the given key.
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IMemoryCache.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IMemoryCache.cs
index 10379bc4cc7a6..88576eba04c74 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IMemoryCache.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/IMemoryCache.cs
@@ -16,7 +16,7 @@ public interface IMemoryCache : IDisposable
         /// <param name="key">An object identifying the requested entry.</param>
         /// <param name="value">The located value or null.</param>
         /// <returns>True if the key was found.</returns>
-        bool TryGetValue(object key, out object value);
+        bool TryGetValue(object key, out object? value);
 
         /// <summary>
         /// Create or overwrite an entry in the cache.
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheEntryExtensions.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheEntryExtensions.cs
index a66d4a519cc4f..ba75e79961012 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheEntryExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheEntryExtensions.cs
@@ -131,7 +131,7 @@ public static MemoryCacheEntryOptions RegisterPostEvictionCallback(
         public static MemoryCacheEntryOptions RegisterPostEvictionCallback(
             this MemoryCacheEntryOptions options,
             PostEvictionDelegate callback,
-            object state)
+            object? state)
         {
             if (callback == null)
             {
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheExtensions.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheExtensions.cs
index 6e3d9422d6310..74d757d76cc24 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/MemoryCacheExtensions.cs
@@ -9,20 +9,20 @@ namespace Microsoft.Extensions.Caching.Memory
 {
     public static class CacheExtensions
     {
-        public static object Get(this IMemoryCache cache, object key)
+        public static object? Get(this IMemoryCache cache, object key)
         {
-            cache.TryGetValue(key, out object value);
+            cache.TryGetValue(key, out object? value);
             return value;
         }
 
-        public static TItem Get<TItem>(this IMemoryCache cache, object key)
+        public static TItem? Get<TItem>(this IMemoryCache cache, object key)
         {
-            return (TItem)(cache.Get(key) ?? default(TItem));
+            return (TItem?)(cache.Get(key) ?? default(TItem));
         }
 
-        public static bool TryGetValue<TItem>(this IMemoryCache cache, object key, out TItem value)
+        public static bool TryGetValue<TItem>(this IMemoryCache cache, object key, out TItem? value)
         {
-            if (cache.TryGetValue(key, out object result))
+            if (cache.TryGetValue(key, out object? result))
             {
                 if (result == null)
                 {
@@ -41,7 +41,7 @@ public static bool TryGetValue<TItem>(this IMemoryCache cache, object key, out T
             return false;
         }
 
-        public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value)
+        public static TItem? Set<TItem>(this IMemoryCache cache, object key, TItem? value)
         {
             using ICacheEntry entry = cache.CreateEntry(key);
             entry.Value = value;
@@ -49,7 +49,7 @@ public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value)
             return value;
         }
 
-        public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value, DateTimeOffset absoluteExpiration)
+        public static TItem? Set<TItem>(this IMemoryCache cache, object key, TItem? value, DateTimeOffset absoluteExpiration)
         {
             using ICacheEntry entry = cache.CreateEntry(key);
             entry.AbsoluteExpiration = absoluteExpiration;
@@ -58,7 +58,7 @@ public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value,
             return value;
         }
 
-        public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value, TimeSpan absoluteExpirationRelativeToNow)
+        public static TItem? Set<TItem>(this IMemoryCache cache, object key, TItem? value, TimeSpan absoluteExpirationRelativeToNow)
         {
             using ICacheEntry entry = cache.CreateEntry(key);
             entry.AbsoluteExpirationRelativeToNow = absoluteExpirationRelativeToNow;
@@ -67,7 +67,7 @@ public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value,
             return value;
         }
 
-        public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value, IChangeToken expirationToken)
+        public static TItem? Set<TItem>(this IMemoryCache cache, object key, TItem? value, IChangeToken expirationToken)
         {
             using ICacheEntry entry = cache.CreateEntry(key);
             entry.AddExpirationToken(expirationToken);
@@ -76,7 +76,7 @@ public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value,
             return value;
         }
 
-        public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value, MemoryCacheEntryOptions options)
+        public static TItem? Set<TItem>(this IMemoryCache cache, object key, TItem? value, MemoryCacheEntryOptions? options)
         {
             using ICacheEntry entry = cache.CreateEntry(key);
             if (options != null)
@@ -89,9 +89,9 @@ public static TItem Set<TItem>(this IMemoryCache cache, object key, TItem value,
             return value;
         }
 
-        public static TItem GetOrCreate<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, TItem> factory)
+        public static TItem? GetOrCreate<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, TItem?> factory)
         {
-            if (!cache.TryGetValue(key, out object result))
+            if (!cache.TryGetValue(key, out object? result))
             {
                 using ICacheEntry entry = cache.CreateEntry(key);
 
@@ -99,12 +99,12 @@ public static TItem GetOrCreate<TItem>(this IMemoryCache cache, object key, Func
                 entry.Value = result;
             }
 
-            return (TItem)result;
+            return (TItem?)result;
         }
 
-        public static async Task<TItem> GetOrCreateAsync<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, Task<TItem>> factory)
+        public static async Task<TItem?> GetOrCreateAsync<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, Task<TItem?>> factory)
         {
-            if (!cache.TryGetValue(key, out object result))
+            if (!cache.TryGetValue(key, out object? result))
             {
                 using ICacheEntry entry = cache.CreateEntry(key);
 
@@ -112,7 +112,7 @@ public static async Task<TItem> GetOrCreateAsync<TItem>(this IMemoryCache cache,
                 entry.Value = result;
             }
 
-            return (TItem)result;
+            return (TItem?)result;
         }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
index f2f695e68eff7..ddd5093c1436a 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/Microsoft.Extensions.Caching.Abstractions.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
     <!-- Use targeting pack references instead of granular ones in the project file. -->
     <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
diff --git a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/PostEvictionCallbackRegistration.cs b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/PostEvictionCallbackRegistration.cs
index 532ffa2385ad0..4c4c950a45569 100644
--- a/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/PostEvictionCallbackRegistration.cs
+++ b/src/libraries/Microsoft.Extensions.Caching.Abstractions/src/PostEvictionCallbackRegistration.cs
@@ -5,8 +5,8 @@ namespace Microsoft.Extensions.Caching.Memory
 {
     public class PostEvictionCallbackRegistration
     {
-        public PostEvictionDelegate EvictionCallback { get; set; }
+        public PostEvictionDelegate? EvictionCallback { get; set; }
 
-        public object State { get; set; }
+        public object? State { get; set; }
     }
 }