DateTime::__construct() expects parameter 1 to be string, array given

[thorau]

My entity has:

     /**
     * @var \DateTime $createdAt
     * @ApiProperty
     * @Groups("read")
     */
     private $createdAt;

    /**
     * @var \DateTime $updatedAt
     * @ApiProperty
     * @Groups("read")
     */
    private $updatedAt;

    /**
     * @return \DateTime
     */
    public function getCreatedAt()
    {
        return $this->createdAt;
    }

    /**
     * @return \DateTime
     */
    public function getUpdatedAt()
    {
        return $this->updatedAt;
    }

    /**
     * @param \DateTime $createdAt
     */
        public function setCreatedAt(\DateTime $createdAt)
    {
        $this->createdAt = $createdAt;
    }

    /**
     * @param \DateTime $updatedAt
     */
    public function setUpdatedAt(\DateTime $updatedAt)
    {
        $this->updatedAt = $updatedAt;
    }

I added to services.yaml:

        class: 'Symfony\Component\Serializer\Serializer'
        arguments:
          - ['@serializer.normalizer.datetime', '@dunglas_doctrine_json_odm.normalizer.object']
          - ['@serializer.encoder.json']
        public: true

But I get the error message:
DateTime::__construct() expects parameter 1 to be string, array given

How to fix this?