how to pass parametere to whereHas clause in laravel

i queryed the Category to get all the id where the 'name', '=', $name and use the result to query Post table

here is the code

public function getList($name){
    $category_id = Category::where('name', '=', $name)
        ->first()->id;
    $posts =Post::whereHas("category", function($q) use ($category_id){
            $q->where('id','=',$category_id);
    })
    ->paginate(12);

    return view('blog.index')
        ->withPosts($posts)
        ->withName($name);
}

but i got this error

ErrorException in Builder.php line 877:
compact(): Undefined variable: operator

Pls how can i solve this issue, its urgent

via Chebli Mohamed