Fix nullable annotations on IW3CActivity

Author: andrewlock

tracer/src/Datadog.Trace/Activity/DuckTypes/IW3CActivity.cs

@@ -11,11 +11,14 @@ namespace Datadog.Trace.Activity.DuckTypes
 {
     internal interface IW3CActivity : IActivity
     {
+        // Note that TraceId and SpanId will not be null when using W3C IDs, but they
+        // _Can_ be nullable when using Hierarchical IDs. Also note that IW3CActivity
+        // could be using _either_ type of ID
         [DuckField(Name = "_traceId")]
-        string TraceId { get; set; }
+        string? TraceId { get; set; }
 
         [DuckField(Name = "_spanId")]
-        string SpanId { get; set; }
+        string? SpanId { get; set; }
 
         [DuckField(Name = "_parentSpanId")]
         string ParentSpanId { get; set; }

tracer/src/Datadog.Trace/Activity/Handlers/AzureServiceBusActivityHandler.cs

@@ -46,15 +46,11 @@ public void ActivityStopped<T>(string sourceName, T activity)
                 // then we can retrieve the active message object using our mapping. With access to the message
                 // object, we can accurately calculate the payload size for the DataStreamsCheckpoint
 
-                ActivityKey key;
-                if (activity is IW3CActivity w3cActivity)
+                ActivityKey key = activity switch
                 {
-                    key = new(w3cActivity.TraceId, w3cActivity.SpanId);
-                }
-                else
-                {
-                    key = new ActivityKey(activity.Id);
-                }
+                    IW3CActivity { TraceId: not null, SpanId: not null } w3cActivity => new(w3cActivity.TraceId, w3cActivity.SpanId),
+                    _ => new(activity.Id)
+                };
 
                 if (key.IsValid() && ActivityHandlerCommon.ActivityMappingById.TryRemove(key, out ActivityMapping activityMapping)
                     && activityMapping.Scope?.Span is Span span)

tracer/src/Datadog.Trace/Activity/Handlers/QuartzActivityHandler.cs

@@ -47,7 +47,7 @@ public void ActivityStopped<T>(string sourceName, T activity)
             // Find the span and update it before the common handler processes it
             ActivityKey key = activity switch
             {
-                IW3CActivity w3cActivity => new(w3cActivity.TraceId, w3cActivity.SpanId),
+                IW3CActivity { TraceId: not null, SpanId: not null } w3cActivity => new(w3cActivity.TraceId, w3cActivity.SpanId),
                 _ => new(activity.Id)
             };