[API] Handle null tracestate values

src/OpenTelemetry.Api/CHANGELOG.md

@@ -11,7 +11,8 @@ Notes](../../RELEASENOTES.md).
 
 * Fixed `TraceContextPropagator` to normalize empty `tracestate` header values
   to `null` when extracting trace context.
-  ([#7407](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7407))
+  ([#7407](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7407),
+  [#7433](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7433))
 
 * **Experimental (pre-release builds only):** Updated `EnvironmentVariableCarrier.Get`
   to read only the normalized environment variable name, following the updated

src/OpenTelemetry.Api/Context/Propagation/TraceContextPropagator.cs

@@ -469,7 +469,7 @@ private static bool TryExtractSingleTracestate(string tracestate, out string tra
     {
         tracestateResult = string.Empty;
 
-        if (tracestate.Length == 0)
+        if (tracestate is not { Length: > 0 })
         {
             return true;
         }

test/OpenTelemetry.Tests/Trace/Propagation/TraceContextPropagatorTests.cs

@@ -336,6 +336,27 @@ public void TryExtractTracestate_NullCollectionReturnsEmpty()
         Assert.Empty(actual);
     }
 
+    [Fact]
+    public void ExtractHandlesNullValue()
+    {
+        var headers = new Dictionary<string, string>
+        {
+            { TraceParent, $"00-{TraceId}-{SpanId}-01" },
+        };
+
+        var propagator = new TraceContextPropagator();
+        var context = propagator.Extract(default, headers, (_, name) => headers.TryGetValue(name, out var value) ? [value] : [null!]);
+
+        Assert.Equal(ActivityTraceId.CreateFromString(TraceId.AsSpan()), context.ActivityContext.TraceId);
+        Assert.Equal(ActivitySpanId.CreateFromString(SpanId.AsSpan()), context.ActivityContext.SpanId);
+
+        Assert.True(context.ActivityContext.IsRemote);
+        Assert.True(context.ActivityContext.IsValid());
+        Assert.NotEqual(0, (int)(context.ActivityContext.TraceFlags & ActivityTraceFlags.Recorded));
+
+        Assert.Null(context.ActivityContext.TraceState);
+    }
+
     [Fact]
     public void Inject_NoTracestate()
     {