refactor: replace 'where' with 'whereNull' for clarity in PurchaseItem queries

app/Http/Controllers/Admin/Manage/PurchaseCartController.php

@@ -14,7 +14,7 @@ public function addToCart(AddToCartRequest $request): RedirectResponse
         $validated = $request->validated();
 
         $item = PurchaseItem::where('user_id', auth()->id())
-            ->where('purchase_id', null)
+            ->whereNull('purchase_id')
             ->where('product_id', $validated['product_id'])
             ->first();
 

app/Http/Controllers/Admin/Manage/PurchaseController.php

@@ -28,7 +28,7 @@ public function create(): Response
             'products' => Product::with(['prices', 'categories'])->active()->get(),
             'cartItems' => PurchaseItem::with(['product.prices', 'product.categories'])
                 ->where('user_id', auth()->id())
-                ->where('purchase_id', null)
+                ->whereNull('purchase_id')
                 ->latest()
                 ->get(),
         ]);
@@ -61,7 +61,7 @@ public function store(PurchaseRequest $request): RedirectResponse
             }
 
             PurchaseItem::where('user_id', auth()->id())
-                ->where('purchase_id', null)
+                ->whereNull('purchase_id')
                 ->delete();
         });
 

resources/js/pages/admin/manage/purchase/edit.tsx

@@ -782,7 +782,6 @@ export default function PurchaseEdit({ purchase, products }: { purchase: Purchas
                     </div>
                 </div>
             </div>
-
             {/* Quantity Input Dialog */}
             <Dialog open={qtyDialogIndex !== null} onOpenChange={(open) => { if (!open) setQtyDialogIndex(null); }}>
                 <DialogContent className="max-w-xs">
@@ -799,7 +798,7 @@ export default function PurchaseEdit({ purchase, products }: { purchase: Purchas
                             value={qtyInputValue}
                             onChange={e => setQtyInputValue(e.target.value)}
                             onKeyDown={e => { if (e.key === 'Enter') confirmQty(); }}
-                            className="text-center text-lg font-bold"
+                            className="text-lg font-bold"
                             autoFocus
                         />
                     </div>