Add debug log.

Author: kinyoklion

sdk/@launchdarkly/observability-dotnet/src/LaunchDarkly.Observability/Observe.cs

@@ -99,7 +99,7 @@ public static void RecordException(Exception exception, IDictionary<string, obje
         {
             if (exception == null)
             {
-                // Silently return if exception is null
+                DebugLogger.DebugLog("An attempt was made to record a null exception.");
                 return;
             }