Symfony - No insertar campos null en Symfony 3

class EntryType extends AbstractType {

    /**

     * {@inheritdoc}

     */

    public function buildForm(FormBuilderInterface $builder, array $options) {

        $builder

                  ->add('image', FileType::class, array(

                    'label' => "Imagen:",

                    'attr' => array("class" => "form-control"),

                    'data_class' => null,

                    'required' => false  //AQUI LO AÑADES

                ))

                ->add('Guardar', SubmitType::class, array(

                    "attr" => array("class" => "form-submit btn btn-success",

            )))

        ;

    }

}

/**

     * @var string

     *

     * @ORM\Column(name="foto", type="blob", length=16777215, nullable=true)

     */

    private $foto;

php bin/console doctrine:generate:entities NombreTuBundle

php bin/console doctrine:schema:update --force

imports:

    - { resource: parameters.yml }

    - { resource: security.yml }

    - { resource: services.yml }

# Put parameters here that don't need to change on each machine where the app is deployed

# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration

parameters:

    locale: en

framework:

    #esi: ~

    translator: { fallbacks: ['%locale%'] }

    secret: '%secret%'

    router:

        resource: '%kernel.project_dir%/app/config/routing.yml'

        strict_requirements: ~

    form: ~

    csrf_protection: ~

    validation: { enable_annotations: true }

    #serializer: { enable_annotations: true }

    templating:

        engines: ['twig']

    default_locale: '%locale%'

    trusted_hosts: ~

    session:

        # https://symfony.com/doc/current/reference/configuration/framework.html#handler-id

        handler_id: session.handler.native_file

        save_path: '%kernel.project_dir%/var/sessions/%kernel.environment%'

    fragments: ~

    http_method_override: true

    assets: ~

    php_errors:

        log: true

# Twig Configuration

twig:

    debug: '%kernel.debug%'

    strict_variables: '%kernel.debug%'

# Doctrine Configuration

doctrine:

    dbal:

        driver: pdo_mysql

        host: '%database_host%'

        port: '%database_port%'

        dbname: '%database_name%'

        user: '%database_user%'

        password: '%database_password%'

        charset: UTF8

        # if using pdo_sqlite as your database driver:

        #   1. add the path in parameters.yml

        #     e.g. database_path: "%kernel.project_dir%/var/data/data.sqlite"

        #   2. Uncomment database_path in parameters.yml.dist

        #   3. Uncomment next line:

        #path: '%database_path%'

    orm:

        auto_generate_proxy_classes: '%kernel.debug%'

        naming_strategy: doctrine.orm.naming_strategy.underscore

        auto_mapping: true

# Swiftmailer Configuration

swiftmailer:

    transport: '%mailer_transport%'

    host: '%mailer_host%'

    username: '%mailer_user%'

    password: '%mailer_password%'

    spool: { type: memory }