title: Sylius\Component\Shipping\Model\ShippingMethodTranslation must be compatible with Sylius\Component\Shipping\Model\ShippingMethod::createTranslation():
body: <p>I'm following the tutorial : "How to customize a translatable Model?" in Sylius doc.</p>
  
  <p>When I run the command : php bin/console doctrine:migrations:diff I got this error :</p>
  
  <p>Fatal error: Declaration of AppBundle\Entity\ShippingMethod::createTranslation(): Sylius\Component\Shipping\Model\ShippingMethodTranslation must be compatible with Sylius\Component\Shipping\Model\ShippingMethod::createTranslation(): Sylius\Component\Shipping\Model\ShippingMethodTranslationInterface in C:\wamp64\www\acme7\src\AppBundle\Entity\ShippingMethod.php on line 8</p>
  
  <p>Here is my class :</p>
  
  <pre><code>&lt;?php
  
  namespace AppBundle\Entity;
  
  use Sylius\Component\Core\Model\ShippingMethod as BaseShippingMethod;
  use Sylius\Component\Shipping\Model\ShippingMethodTranslation;
  
  class ShippingMethod extends BaseShippingMethod
  {
      /**
       * @var string
       */
       private $estimatedDeliveryTime;
  
      /**
       * @return string
       */
      public function getEstimatedDeliveryTime(): string
      {
          return $this-&gt;estimatedDeliveryTime;
      }
  
      /**
       * @param string $estimatedDeliveryTime
       */
      public function setEstimatedDeliveryTime(string $estimatedDeliveryTime): void
      {
           $this-&gt;estimatedDeliveryTime = $estimatedDeliveryTime;
      }
  
      /**
       * {@inheritdoc}
       */
       protected function createTranslation(): ShippingMethodTranslation
       {
      return new ShippingMethodTranslation();
       }
  }
  </code></pre>
  
  <p>Any idea on how to solved this ?</p>