Gender.orm.yml

SharedKernel\Domain\Model\Gender:
    type: embeddable
    fields:
        value: { type: string, length: 8, column: gender, nullable: true }

Gender.php

<?php

declare(strict_types=1);

namespace SharedKernel\Domain\Model;

use Assert\Assertion;

/**
 * Class Gender
 * @package SharedKernel\Domain\Model
 */
class Gender implements \Tarifhaus\Doctrine\ORM\NullableEmbeddableInterface
{
    /**
     * @var string
     */
    private $value;

    /**
     * @param string $gender
     */
    public function __construct(string $gender)
    {
        $gender = strtolower($gender);

        Assertion::inArray($gender, ['male', 'female']);

        $this->value = $gender;
    }

    /**
     * @return string
     */
    public function getValue(): string
    {
        return $this->value;
    }

    /**
     * @return string
     */
    public function __toString(): string
    {
        return $this->getValue();
    }

    /**
     * @return bool
     */
    public function isNull(): bool
    {
        return $this->value === null;
    }
}

User.orm.yml

User\Domain\Model\User:
    type: entity
    table: users
    id:
        id:
            type: userId
            length: 36
            nullable: false
            generator:
                strategy: NONE
                
    embedded:
        gender:
            class: SharedKernel\Domain\Model\Gender
            columnPrefix: false

@szepczynski You would have to call $listener->addMapping('User\Domain\Model\User', 'gender'); and the listener has to be registered with postLoad event of the User\Domain\Model\User entity.

If you are using Symfony, the service definition would be something like:

services:
    tarifhaus.doctrine.nullable_embeddable_listener:
        public: false
        class: Tarifhaus\Doctrine\ORM\NullableEmbeddableListener
        arguments:
            - '@property_accessor'
        calls:
            - ['addMapping', ['User\Domain\Model\User', 'gender']]
        tags:
            - { name: 'doctrine.orm.entity_listener', entity: 'User\Domain\Model\User', event: 'postLoad' }

I will add a README with an example to the repository :)

Could you proof-read the README, I just added, are there any details missing? - https://github.com/tarifhaus/doctrine-nullable-embeddable/blob/master/README.md