Sonata Media Bundle Custom Provider not mapping request data

I have a custom ImageProvider to use with Sonata's Media Bundle.

Unfortunetly when I click submit, the form fields are placed into extra_data rather than the form object resulting in the error message This form should not contain extra fields..

My buildCreateForm function is as follows:

    public function buildCreateForm(FormMapper $formMapper)
    {
        $formMapper
            ->with('Media Details', ['class' => 'panel-media-details'])
                ->add('binaryContent', 'file', [
                    'label' => 'Upload an Image File',
                    'help'  => AdminUtils::helpPopover(
                        'The uploaded image file should be in one of the following types: <strong>png, gif, jpg, jpeg</strong>',
                        ['placement' => 'right']
                    ),
                    'constraints' => [
                        new NotBlank(),
                        new NotNull(),
                        new File([
                            'mimeTypes' => ['image/png', 'image/gif', 'image/jpeg', 'image/pjpeg'],
                            'mimeTypesMessage' => 'This file is not an image (should be a PNG, a GIF or a JPEG, but is a {{ type }})',
                        ])
                    ],
                ])
                ->add('name', 'text', [
                    'label' => 'Title',
                    'help'  => AdminUtils::helpPopover(
                        'The title for the image. It will be displayed as the image caption when embedding the image in text or when rendering it as part of a gallery. It will also be displayed as the title on the individual media item page, and in search results.',
                        ['placement' => 'right']
                    ),
                    'required' => true,
                ])
                ->add('alt_tag', 'text', [
                    'label' => 'Alternative Text',
                    'help'  => AdminUtils::helpPopover(
                        'The text that will be used by screen readers, search engines, and when the image cannot be loaded. If not provided, the title will be used.',
                        ['placement' => 'right']
                    ),
                    'mapped'   => false,
                    'required' => true,
                ])
                ->add('description', CKEditorType::class, [
                    'help'     => AdminUtils::helpPopover('The description will be displayed on the media item page, in search results, and possibly when the image is displayed in a popup (lightbox) by itself or as part of a media gallery.', ['placement' => 'right']),
                    'required' => false,
                ])
            ->end()

            ->with('Notes', ['class' => 'panelr-notes'])
                ->add('notes', CKEditorType::class, [
                    'label'    => 'Notes',
                    'help'     => AdminUtils::helpPopover('Notes for administrative purposes; these are visible to Editors only and they will never be displayed on the frontend site.'),
                    'required' => false,
                ])
            ->end()

        ;
    }

My $mediaAdmin->configureFormFields() looks like this:

    protected function configureFormFields(FormMapper $formMapper)
    {
        $formMapper
            ->with('Publishing', ['class' => 'panelr-publishing'])
                ->add('enabled', null, [
                    'label'    => 'Published',
                    'help'     => AdminUtils::helpPopover('Media items that are unpublished will not be displayed anywhere on the frontend site, even when they are attached to content or embedded into text. They will still be visible in the backend CMS site.'),
                    'required' => false,
                ])
            ->end()
        ;

        $media = $this->getSubject();

        if (!$media) {
            $media = $this->getNewInstance();
        }

        if (!$media || !$media->getProviderName()) {
            return;
        }

        $formMapper->getFormBuilder()->addModelTransformer(
            new ProviderDataTransformer($this->pool, $this->getClass()), true
        );

        $provider = $this->pool->getProvider($media->getProviderName());

        if ($media->getId()) {
            $provider->buildEditForm($formMapper);
        } else {
            $provider->buildCreateForm($formMapper);
        }

        // Put any hidden fields at the bottom of the form so that they don't
        // break :first-child css rules used. Also, wrap them in a closed form
        // group so that it doesn't break form groups loaded through
        // buildEditForms or configureFormFields defined in child Admin classes.
        $formMapper
            ->with('Provider', ['class' => 'hidden-provider'])
                ->add('providerName', 'hidden')
            ->end()
        ;
    }

and the debug of the form object after failing validation is:

I am overriding the sonata.media.provider.iamge hence that being shown as the provider.

For those who find there way here...

First, to get passed the extra fields violation

public function getFormBuilder()
{
    $this->formOptions['allow_extra_fields'] = true;
    return parent::getFormBuilder();
}

next to manually map the fields

public function prePersist($media)
{
    // This is a bit messy, but get the extra_data array and manually map it
    $extraData = $this->getForm()->getExtraData();
    $media->setProviderName($extraData['providerName']);

    $media->setName($extraData['name']);
    $media->setDescription($extraData['description']);
    $media->setBinaryContent($extraData['binaryContent']);
    $media->setNotes($extraData['notes']);

   parent::prePersist($media);
}