При создании поста в Панели Администратора выдаёт ошибку. AdminLTE Version 2.3.7, Laravel 5.4.36

(1/1) ErrorException join(): Passing glue string after array is deprecated. Swap the parameters

in SlugService.php (line 137)

at HandleExceptions->handleError()

at join() in SlugService.php (line 137)

Post.php

    public static function add($fields)
    {
        $post = new static;
        $post->fill($fields);
        $post->user_id = Auth::user()->id;
        $post->save();

        return $post;
    }