Improve asset sorting by brand, model, and QR code with null handling

src/main/java/be/seeseepuff/pcinv/controllers/WebController.java

@@ -96,7 +96,10 @@ public class WebController {
         model.addAttribute(DESCRIPTORS, tree);
         model.addAttribute(PROPERTIES, tree.stream().flatMap(d -> d.getProperties().stream()).toList());
         var assets = assetService.getAssetsByType(type);
-        assets.sort(Comparator.comparing(Asset::getQr));
+        assets.sort(Comparator
+                .comparing((Asset a) -> a.getAsset().getBrand(), Comparator.nullsFirst(Comparator.naturalOrder()))
+                .thenComparing((Asset a) -> a.getAsset().getModel(), Comparator.nullsFirst(Comparator.naturalOrder()))
+                .thenComparing(Asset::getQr));
         model.addAttribute(ASSETS, assets);
         return "browse_type";
     }