Why larastan raised error on relation method?

In laravel 11 with larastan/larastan 2.9 app I with request :

$managers = ModelHasPermission
    ::getByPermissionId(PERMISSION_APP_MANAGER)
    ->with('user') // ERROR POINTING THIS LINE 37
    ->get();
foreach ($managers as $manager) {
    $manager->user->notify(new ContactUsSentNotification(contactUs: $contactUs, manager: $manager->user));
}

Running larastan with level = 6 I got error :

37     Relation 'user' is not found in App\Models\ModelHasPermission model.
43     Access to an undefined property App\Models\ModelHasPermission::$user.
💡 Learn more: https://phpstan.org/blog/solving-phpstan-access-to-undefined-property
43     Access to an undefined property App\Models\ModelHasPermission::$user.
💡 Learn more: https://phpstan.org/blog/solving-phpstan-access-to-undefined

But In model app/Models/ModelHasPermission.php I have :

<?php

namespace App\Models;

use DB;
use Illuminate\Database\Eloquent\Model;

class ModelHasPermission extends Model
{
    protected $table      = 'model_has_permissions';
    protected $primaryKey = 'id';

    ...

    public function user()
    {
        return $this->belongsTo(User::class, 'model_id');
    }


}

How have I to define user method not to have this/and next on line 43 Access to an undefined property errors ?

Thanks to kris, this solved the problem

  public function user(): BelongsTo
    {
        return $this->belongsTo(User::class, 'model_id');
    }