Handle empty TenantId gracefully in OpenAI client creation

Co-authored-by: diberry <41597107+diberry@users.noreply.github.com>

Author: Copilot

ai/vector-search-dotnet/Services/EmbeddingService.cs

@@ -24,10 +24,12 @@ public EmbeddingService(
 
         try
         {
-            var credential = new DefaultAzureCredential(new DefaultAzureCredentialOptions
+            var credentialOptions = new DefaultAzureCredentialOptions();
+            if (!string.IsNullOrEmpty(_config.AzureOpenAI.TenantId))
             {
-                TenantId = _config.AzureOpenAI.TenantId
-            });
+                credentialOptions.TenantId = _config.AzureOpenAI.TenantId;
+            }
+            var credential = new DefaultAzureCredential(credentialOptions);
             _openAIClient = new AzureOpenAIClient(
                 new Uri(_config.AzureOpenAI.Endpoint),
                 credential);

ai/vector-search-dotnet/Services/VectorSearchService.cs

@@ -28,10 +28,12 @@ public VectorSearchService(ILogger<VectorSearchService> logger, MongoDbService m
         _config = config;
 
         // Initialize Azure OpenAI client with passwordless authentication
-        var credential = new DefaultAzureCredential(new DefaultAzureCredentialOptions
+        var credentialOptions = new DefaultAzureCredentialOptions();
+        if (!string.IsNullOrEmpty(_config.AzureOpenAI.TenantId))
         {
-            TenantId = _config.AzureOpenAI.TenantId
-        });
+            credentialOptions.TenantId = _config.AzureOpenAI.TenantId;
+        }
+        var credential = new DefaultAzureCredential(credentialOptions);
         _openAIClient = new AzureOpenAIClient(new Uri(_config.AzureOpenAI.Endpoint), credential);
     }