fix: return empty array for null or empty results in EnhanceDetailsResults and EnhanceSearchResults methods

Author: jongalloway

src/NLWebNet/Services/DetailsToolHandler.cs

@@ -143,7 +143,7 @@ private string ExtractSubject(string query)
     private IList<NLWebResult> EnhanceDetailsResults(IList<NLWebResult> results, string subject)
     {
         if (results == null || !results.Any())
-            return results;
+            return Array.Empty<NLWebResult>();
 
         // Filter and rank results by their detail relevance
         var detailResults = results

src/NLWebNet/Services/SearchToolHandler.cs

@@ -113,7 +113,7 @@ private Task<string> OptimizeSearchQuery(string query, CancellationToken cancell
     private IList<NLWebResult> EnhanceSearchResults(IList<NLWebResult> results, string originalQuery)
     {
         if (results == null || !results.Any())
-            return results;
+            return Array.Empty<NLWebResult>();
 
         // Sort results by relevance (simple implementation)
         var sortedResults = results