title: Class does not implement "Symfony\Component\Form\FormTypeInterface" in Sylius
body: <p>We are trying to extend from <code>CustomerProfileType</code> and we are getting error like:</p>
  
  <pre><code> {
  "code": 500,
  "message": "Could not load type "abc\Form\Extension\AdminApi\CustomerProfileTypeExtension": class does not implement "Symfony\Component\Form\FormTypeInterface"."
  }
  </code></pre>
  
  <p>Customer.yml:</p>
  
  <pre><code>sylius_admin_api_customer_create:
      path: /
      methods: [POST]
      defaults:
          _controller: sylius.controller.customer:createAction
          _sylius:
              serialization_version: $version
              serialization_groups: [Detailed]
              form:
                  type: abc\Form\Extension\AdminApi\CustomerProfileTypeExtension
  </code></pre>
  
  <p>CustomerProfileTypeExtension.php</p>
  
  <pre><code>final class CustomerProfileTypeExtension extends AbstractTypeExtension
  {
      /**
       * {@inheritdoc}
       */
      public function buildForm(FormBuilderInterface $builder, array $options): void
      {
          // Adding new fields works just like in the parent form type.
          $builder-&gt;add('contactHours', TextType::class, [
              'required' =&gt; false,
              'label' =&gt; 'app.form.customer.contact_hours',
          ]);
  
          // To remove a field from a form simply call -&gt;remove(`fieldName`).
          $builder-&gt;remove('gender');
  
          // You can change the label by adding again the same field with a changed `label` parameter.
          $builder-&gt;add('lastName', TextType::class, [
              'label' =&gt; 'app.form.customer.surname',
          ]);
      }
  
  
      /**
       * {@inheritdoc}
       */
      public function getExtendedType(): string
      {
          return CustomerProfileType::class;
      }
  
  
  }
  </code></pre>