public function store(Request $request){      $article = Article::create($request->only(['content']));    $categories = explode(",",$request->get('categories'));    $category_ids =[];    foreach ($categories as $category) {        $category_db = Category::where('name', trim($category))->firstOrCreate(['name'=> trim($category)]);        $category_ids [] = $category_db->id;    }    $article->category()->attach($category_ids);    return response("Successfully Added to Database");}最后沒有逗號也沒有問題 ， 在數據庫中一切都很好現在的問題是，當我在末尾放一個逗號時，數據庫中會創建一個帶有空格的單元格我知道為什么會這樣。包含值的分解數組的最后一個鍵是空格。但我想省略或留下那個空鑰匙。我怎樣才能做到這一點？