I have a problem when I'm trying to create an EntityType field in my Symfony2 form type.

This is the piece of code from the official EntityType reference in Symfony2 manual:

```
use Symfony\Bridge\Doctrine\Form\Type\EntityType; 

...

$builder->add('users', EntityType::class, array(
        'class' => 'AppBundle:User',
        'choice_label' => 'username',
    ));

```

Going back to the browser I'm getting the `Could not load type "Symfony\Bridge\Doctrine\Form\Type\EntityType"` error.

The EntityType class exist in the given namespespace. 

Do I need to get some aditional extensions for this field type?