### whereNull 方法筛选给定键为 NULL 的项 whereNull 方法筛选给定键为 NULL 的项： ``` $collection = collect([ ['name' => 'Desk'], ['name' => null], ['name' => 'Bookcase'], ]); $filtered = $collection->whereNull('name'); $filtered->all(); /* [ ['name' => null], ] */ ```