Apply suggestion from @mikekistler

Co-authored-by: Mike Kistler <mikekistler@microsoft.com>

Author: halter73

src/ModelContextProtocol/McpServerHandlers.cs

@@ -189,6 +189,7 @@ internal void OverwriteWithSetHandlers(McpServerOptions options)
 
         if (SubscribeToResourcesHandler is not null || UnsubscribeFromResourcesHandler is not null)
         {
+            resourcesCapability ??= new();
             resourcesCapability.SubscribeToResourcesHandler = SubscribeToResourcesHandler ?? resourcesCapability.SubscribeToResourcesHandler;
             resourcesCapability.UnsubscribeFromResourcesHandler = UnsubscribeFromResourcesHandler ?? resourcesCapability.UnsubscribeFromResourcesHandler;
             resourcesCapability.Subscribe = true;