Как правильно вылечить эту ошибку: could not be converted to string?

Catchable Fatal Error: Object of class App\Entity\Account could not be converted to string

<?php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity(repositoryClass="App\Repository\AccountRepository")
 */
class Account
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private $benutzer;

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

    public function getBenutzer(): ?string
    {
        return $this->benutzer;
    }

    public function setBenutzer(string $benutzer): self
    {
        $this->benutzer = $benutzer;

        return $this;
    }


    public function __toString(){
        // to show the name of the Category in the select
        return $this->benutzer;
    }

}

<?php

namespace App\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity(repositoryClass="App\Repository\MenschenRepository")
 */
class Menschen
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\ManyToMany(targetEntity="App\Entity\Account")
     */
    private $account;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private $vorname;

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

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

    /**
     * @return Collection|Account[]
     */
    public function getAccount(): Collection
    {
        return $this->account;
    }

    public function addAccount(Account $account): self
    {
        if (!$this->account->contains($account)) {
            $this->account[] = $account;
        }

        return $this;
    }

    public function removeAccount(Account $account): self
    {
        if ($this->account->contains($account)) {
            $this->account->removeElement($account);
        }

        return $this;
    }

    public function getVorname(): ?string
    {
        return $this->vorname;
    }

    public function setVorname(string $vorname): self
    {
        $this->vorname = $vorname;

        return $this;
    }
}

public function __toString(){
        return $this->benutzer;
    }