Erro no buscar-alunos.php

PHP Notice:  Undefined index: Aluno in /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php on line 1821
PHP Warning:  Invalid argument supplied for foreach() in /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php on line 1825
PHP Notice:  Undefined index: Aluno in /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/PersistentCollection.php on line 157
PHP Fatal error:  Uncaught Error: Call to a member function setValue() on null in /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/PersistentCollection.php:157
Stack trace:
#0 /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php(500): Doctrine\ORM\PersistentCollection->hydrateAdd(Object(Alura\Doctrine\Entity\Telefone))
#1 /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php(143): Doctrine\ORM\Internal\Hydration\ObjectHydrator->hydrateRowData(Array, Array)
#2 /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Internal/Hydration/AbstractHydrator.php(270): Doctrine\ORM\Internal\Hydration\ObjectHydrator->hydrateAllData()
#3 /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php(977): Doctrine\ORM\Internal\Hydration\AbstractHydrator->hydrateAll(Object(Doctrine\DBAL\ForwardCompatibility\Result), Object(Doctrine\OR in /mnt/c/Dev/web/meu_dominio/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/PersistentCollection.php on line 157

<?php

namespace Alura\Doctrine\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Alura\Doctrine\Entity\Telefone;

/** 
 * @Entity
 */
class Aluno
{
    /**
     * @Id
     * @GeneratedValue
     * @Column(type="integer")
     */
    private $id;
    /**
     * @Column(type="string")
     */
    private $nome;
    /**
     * @OneToMany(targetEntity="Telefone", mappedBy="Aluno", cascade={"remove", "persist"})
     */
    private $telefones;

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


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

    public function getNome(): string
    {
        return $this->nome;
    }

    public function setNome($nome): self
    {
        $this->nome = $nome;
        return $this;
    }

    public function addTelefone(Telefone $telefone)
    {
        $this->telefones->add($telefone);
        $telefone->setAluno($this);
        return $this;
    }

    public function getTelefones(): Collection
    {
        return $this->telefones;
    }
}

<?php

namespace Alura\Doctrine\Entity;

use Alura\Doctrine\Entity\Aluno;

/**
 * @Entity
 */
class Telefone
{
    /**
     * @Id
     * @GeneratedValue
     * @Column(type="integer")
     */
    private $id_telefone;
    /**
     * @Column(type="string")
     */
    private $numero;
    /**
     * @ManyToOne(targetEntity="Aluno")
     */
    private $aluno;

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

    public function getNumero(): string
    {
        return $this->numero;
    }

    public function setNumero($numero): self
    {
        $this->numero = $numero;
        return $this;
    }

    public function setAluno(Aluno $aluno)
    {
        $this->aluno = $aluno;
        return $this;
    }

    public function getAluno(): Aluno
    {
        return $this->aluno;
    }
}