fix(products): keep category when update sends null product_categories_id

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/Http/Controllers/Api/Admin/Product/ProductController.php

@@ -173,6 +173,10 @@ class ProductController extends Controller
             'features'              => 'nullable|array',
         ]);
 
+        if (array_key_exists('product_categories_id', $validated) && $validated['product_categories_id'] === null) {
+            unset($validated['product_categories_id']);
+        }
+
         if (isset($validated['name']) && $validated['name'] !== $product->name) {
             $validated['slug'] = Str::slug($validated['name']);
         }

tests/Feature/Api/Admin/Product/ProductUpdateCategoryTest.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature\Api\Admin\Product;
+
+use App\Models\Product;
+use App\Models\ProductCategories;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Spatie\Permission\Models\Role;
+use Tests\TestCase;
+
+class ProductUpdateCategoryTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_null_category_keeps_existing_category(): void
+    {
+        Role::firstOrCreate(['name' => 'Full Administrator', 'guard_name' => 'admin']);
+        $admin = User::factory()->create();
+        $admin->assignRole('Full Administrator');
+        $category = ProductCategories::create(['name' => 'VPS', 'slug' => 'vps', 'is_active' => true, 'sort_order' => 1]);
+        $product = Product::factory()->create(['product_categories_id' => $category->id]);
+
+        $this->actingAs($admin, 'admin')
+            ->putJson("/api/v1/administrator/products/{$product->id}", [
+                'name' => 'Renamed',
+                'product_categories_id' => null,
+            ])
+            ->assertOk();
+
+        $this->assertSame($category->id, $product->fresh()->product_categories_id);
+    }
+}