cakephp: Undefined index in entity properties for new entity

This is a (multiple allowed):

• bug

• enhancement

• feature-discussion (RFC)

• CakePHP Version: 3.6.4.

• Platform and Target: Apache / MySQL.

What you did

I wrote the following reusable Trait for Users:

namespace App\Model\Traits;
trait UsersPropertiesTrait
{

    /**
     * Return fullName of contact.
     *
     * @return string
     */
    protected function _getFullName()
    {
        return $this->_properties['first_name'] . '  ' . $this->_properties['last_name'];
    }

    /**
     * Return fullName + email.
     *
     * @return string
     */
    protected function _getFullLabel()
    {
        return $this->_getFullName() . '  (' . $this->_properties['email'] . ')';
    }
}

Entity code for Users, based on CakeDC Users Class:

namespace App\Model\Entity;

use App\Model\Traits\UsersPropertiesTrait;
use CakeDC\Users\Model\Entity\User;

class MyUser extends User
{
    use UsersPropertiesTrait;

    /**
     * Fields that can be mass assigned using newEntity() or patchEntity().
     *
     * Note that when '*' is set to true, this allows all unspecified fields to
     * be mass assigned. For security purposes, it is advised to set '*' to false
     * (or remove it), and explicitly make individual fields accessible as needed.
     *
     * @var array
     */
    protected $_accessible = [
        '*' => true,
        'id' => false
    ];

    /**
     * Fields that are excluded from JSON versions of the entity.
     *
     * @var array
     */
    protected $_hidden = [
        'password',
        'token'
    ];

    protected $_virtual = ['full_label', 'full_name'];
}

The virtual properties are working if the data already exists. But since my upgrade to 3.6.4, it doesn’t work with a new entity.

What happened

Undefined index: first_name in [/var/www/html/charlie/src/Model/Traits/UsersPropertiesTrait.php, line 14]

The new entity hasn’t the expected keys.

What you expected to happen

What can i do to make this work again ?