If you are using the Laravel factories to populate the database with fake elements, when you add a new factory, v.gr. in the «\database\factories\ModelFactory.php», ant try to execute it with the tinker app
$ php artisan tinker >>> factory(App\Contrato::class, 100)->create();
you can receive this error (for the «Contrato» model).
InvalidArgumentException with message 'Unable to locate factory with name [default] [App\Contrato].'
This could be a cache problem. You can resolve it executing the commands showed in this link.
php artisan clear-compiled composer dump-autoload php artisan optimize