Doctrine related entities return all fields values NULL

I am using Symfony 3.1.10 on a server with PHP 5.6.31 (with Zend OPcache 7.0.6-dev), Apache and MySQL (Ver 14.14 Distrib 5.6.37).

I have an Entity called Document with a related Entity called Worker

The relationship have always worked untill today... Non when I retrive a document with a worker, all the worker field are null (except the ID).

So if in my DB there is a worker with fields: id 4, name: John, age: 33 if I retrive a document with this worker relater and dump $document->getWorker() i return an objet Worker with id: 4, name: null, age: null.

The Document class

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
* @ORM\Entity
* @ORM\Table(name="documents")
* @ORM\Entity(repositoryClass="AppBundle\Repository\DocumentRepository")
*/
class Document
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\Column(type="string", nullable=true)
     */
    protected $object;

    /**
     * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Worker", cascade={"persist"}, inversedBy="documents")
     * @ORM\JoinColumn(name="worker_id", referencedColumnName="id", onDelete="SET NULL")
     */
    protected $worker;

    public function getId()
    {
        return $this->id;
    }

    public function setObject($object)
    {
        $this->object = $object;

        return $this;
    }

    public function getObject()
    {
        return $this->object;
    }

    public function setWorker(\AppBundle\Entity\Worker $worker = null)
    {
        $this->worker = $worker;

        return $this;
    }

    public function getWorker()
    {
        return $this->worker;
    }
}

The worker class

namespace AppBundle\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints AS Assert;

/**
* @ORM\Entity
* @ORM\Table(name="workers")
* @ORM\Entity(repositoryClass="AppBundle\Repository\WorkerRepository")
*/
class Worker
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\Column(type="string", nullable=true)
     * @Assert\NotBlank()
     */
    protected $firstName;

    /**
     * @ORM\Column(type="string", nullable=true)
     * @Assert\NotBlank()
     */
    protected $lastName;

    /**
     * @ORM\Column(type="string", nullable=true)
     * @Assert\NotBlank()
     */
    protected $age;

    /**
     * @ORM\OneToMany(targetEntity="AppBundle\Entity\Document", mappedBy="worker")
     */
    protected $documents;

    public function __construct()
    {
        $this->documents = new ArrayCollection();
    }

    public function __toString() {
        return $this->firstName . ' ' . $this->lastName;
    }

    public function getId()
    {
        return $this->id;
    }

    public function setFirstName($firstName)
    {
        $this->firstName = $firstName;

        return $this;
    }

    public function getFirstName()
    {
        return $this->firstName;
    }

    public function setLastName($lastName)
    {
        $this->lastName = $lastName;

        return $this;
    }

    public function getLastName()
    {
        return $this->lastName;
    }

    public function setAge($age)
    {
        $this->age = $age;

        return $this;
    }

    public function getAge()
    {
        return $this->age;
    }

    public function addDocument(\AppBundle\Entity\Document $document)
    {
        $this->documents[] = $document;

        return $this;
    }

    public function removeDocument(\AppBundle\Entity\Document $document)
    {
        $this->documents->removeElement($document);
    }

    public function getDocuments()
    {
        return $this->documents;
    }
}

I read here: Doctrine always return null values in production

I tried everything, but nothing works.