diff --git a/docs/building.md b/docs/building.md
index 5d042c9bf87..b7845cd6945 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -157,6 +157,15 @@ This sets up necessary environmental variables and opens the repository in VS Co
 * When restoring packages, if you get the following message: "The SSL connection could not be established, see inner exception. Unable to read data from the transport connection", try disabling IPv6 on your network adapter.
 * When the public API surface is updated, you need to update the API baselines manifest files for the impacted assemblies. [Here is an example](https://github.com/dotnet/extensions/blob/3e6ac0735cb62d4c8b63e131d956397a87ea26f7/src/Libraries/Microsoft.Extensions.AsyncState/Microsoft.Extensions.AsyncState.json) for the `Microsoft.Extensions.AsyncState` project. To update the manifest of all the local assemblies, invoke the script `./scripts/MakeApiBaselines.ps1`.
 
+#### How to fix "Workload manifest microsoft.net.sdk.aspire not installed"?
+
+At times, during restore you may receive the following error:
+```
+error MSB4242: SDK Resolver Failure: "The SDK resolver "Microsoft.DotNet.MSBuildWorkloadSdkResolver" failed while attempting to resolve the SDK "Microsoft.DotNet.Arcade.Sdk".
+Exception: "System.IO.FileNotFoundException: Workload manifest microsoft.net.sdk.aspire: 8.0.1/8.0.100 from workload version <x.y.z> was not installed. Running "dotnet workload repair" may resolve this.
+```
+
+This error is, generally, caused by multiple SDK installations under \<root\>/.dotnet folder. To resolve the issue, run `git clean -xdf` and then run restore again.
 
 ---
 
diff --git a/src/Libraries/Microsoft.Extensions.TimeProvider.Testing/Timer.cs b/src/Libraries/Microsoft.Extensions.TimeProvider.Testing/Timer.cs
index c6d7bf5ab1f..926e500166f 100644
--- a/src/Libraries/Microsoft.Extensions.TimeProvider.Testing/Timer.cs
+++ b/src/Libraries/Microsoft.Extensions.TimeProvider.Testing/Timer.cs
@@ -37,16 +37,18 @@ public bool Change(TimeSpan dueTime, TimeSpan period)
         _ = Throw.IfOutOfRange(periodMs, -1, MaxSupportedTimeout, nameof(period));
 #pragma warning restore S3236 // Caller information arguments should not be provided explicitly
 
-        if (_timeProvider == null)
+        var timeProvider = _timeProvider;
+        if (timeProvider is null)
         {
             // timer has been disposed
             return false;
         }
 
-        if (_waiter != null)
+        var waiter = _waiter;
+        if (waiter is not null)
         {
             // remove any previous waiter
-            _timeProvider.RemoveWaiter(_waiter);
+            timeProvider.RemoveWaiter(waiter);
             _waiter = null;
         }
 
@@ -62,8 +64,8 @@ public bool Change(TimeSpan dueTime, TimeSpan period)
             period = TimeSpan.Zero;
         }
 
-        _waiter = new Waiter(_callback!, _state, period.Ticks);
-        _timeProvider.AddWaiter(_waiter, dueTime.Ticks);
+        _waiter = waiter = new Waiter(_callback!, _state, period.Ticks);
+        timeProvider.AddWaiter(waiter, dueTime.Ticks);
         return true;
     }
 
@@ -89,9 +91,10 @@ public ValueTask DisposeAsync()
 
     private void Dispose(bool _)
     {
-        if (_waiter != null)
+        var waiter = _waiter;
+        if (waiter is not null)
         {
-            _timeProvider!.RemoveWaiter(_waiter);
+            _timeProvider?.RemoveWaiter(waiter);
             _waiter = null;
         }