Context
-------

I'm currently trying to add file relation to an entity of my OroPlatform project.
The goal is to give the opportunity to the user to upload files on the create/update view of a specific entity.

I have read in the OroPlatform documentation that I have to create a new migration : <https://doc.oroinc.com/master/backend/bundles/platform/AttachmentBundle/attachment-bundle-config/#attachment-bundle-file-types>

Here is the migration I have created :

```php
<?php

namespace Baltimore\Bundle\AppBundle\Migrations\Schema\v1_1_1;

use Doctrine\DBAL\Schema\Schema;

use Oro\Bundle\AttachmentBundle\Migration\Extension\AttachmentExtension;
use Oro\Bundle\AttachmentBundle\Migration\Extension\AttachmentExtensionAwareInterface;
use Oro\Bundle\MigrationBundle\Migration\Migration;
use Oro\Bundle\MigrationBundle\Migration\QueryBag;

class AddAttachmentToBusinessUnit implements Migration, AttachmentExtensionAwareInterface
{
    /** @var AttachmentExtension */
    protected $attachmentExtension;

    /**
     * {@inheritdoc}
     */
    public function setAttachmentExtension(AttachmentExtension $attachmentExtension)
    {
        $this->attachmentExtension = $attachmentExtension;
    }

    /**
     * {@inheritdoc}
     */
    public function up(Schema $schema, QueryBag $queries)
    {
        $this->attachmentExtension->addFileRelation(
            $schema,
            'oro_business_unit',
            'document',
            [],
            15
        );
    }
}

```

And I have added this line to the `update.html.twig` of my entity: `form_row(form.document)`

Issue
-----

When I try to access the update page, I have the following error :

```
"Neither the property "document" nor one of the methods "document()", "getdocument()"/"isdocument()"/"hasdocument()" or "__call()" exist and have public access in class "Symfony\Component\Form\FormView"."

```

I have warmup the cache in order to generate the accessors for my class and the method `getDocument()` exist in the generated file `EX_OroOrganizationBundle_BusinessUnit.php`

Also, it seems that the property has been successfully added to my entity :

[![enter image description here](https://i.stack.imgur.com/gWtuh.png)](https://i.stack.imgur.com/gWtuh.png)