[Sylius] Argument 1 passed to Sylius\Component\Grid\Definition\Filter::setTemplate() must be of the type string, null given fix

 put `grid: <gridname>` into your route like this:

tests:
    path: /tests
    defaults:
        _controller: app.controller.test:indexAction
        _sylius:
            template: tests/index.html.twig
            grid: app_test

[Monofony] how to create/get admin user?

 run `php bin/console app:install:database`, after then you will have user "admin@example.com" with password "admin". You can use it in 127.0.0.1:8000/admin/login

[Vue] [vee-validate] collection.indexOf is not a function - how to fix

 It occurs when to get error message (with `errors.first('myfield')`) of not existing field. In another words, check that component field has v-validate tag attribute (and maybe also `name` attribute). Or remove `errors.first('myfield')` line at all, this will fix this error.