BadMethodCallException调用未定义的方法App \ Models \ Menu :: menu（）

I have 'Menus' table and this website is for a restaurant. When I add a new record through Laravel Backpack Crud, it gives me an error

BadMethodCallException Call to undefined method App\Models\Menu::menu()

however, it adds the record to DB. When I want to update some record, it gives me this error but does not update the DB. Where can be the problem?

Here is my model:

<?php

namespace App\Models;

use Backpack\CRUD\CrudTrait;
use Illuminate\Database\Eloquent\Model;

class Menu extends Model
{
    use CrudTrait;

    protected $table = 'menus';
    protected $fillable = ['image', 'name', 'description', 'price', 'category_id', 'popular'];



    public function category()
    {
        return $this->belongsTo(Category::class);
    }

Category.php:

<?php

namespace App\Models;

use Backpack\CRUD\CrudTrait;
use Illuminate\Database\Eloquent\Model;

class Category extends Model
{
    use CrudTrait;

    protected $table = 'categories';



    public function menu()
    {
        return $this->hasMany(Menu::class);
    }

MenuCrudController:

/*
        |--------------------------------------------------------------------------
        | CrudPanel Basic Information
        |--------------------------------------------------------------------------
        */
        $this->crud->setModel('App\Models\Menu');
        $this->crud->setRoute(config('backpack.base.route_prefix') . '/menu');
        $this->crud->setEntityNameStrings('menu', 'menus');