Symfony, property is not recognised, "Notice: Undefined property:..."

[gintare]

I am following Udemy course:
https://www.udemy.com/introduction-to-web-development-with-symfony2/#/lecture/933836

There is Post model with several fields: title, author, body;
which inherits from Timestampable model with field: createdAt.

When i try to display Post model in template, the Author and post are displayed, but field "createdAt" is not recognised and gives error "Notice: Undefined property: Blog\ModelBundle\Entity\Post::$createdAt".
(I comment out "createdAt" in template and than Author, title and post are displayed. )


_post.html.twig:

<article>
 
    <header><h2><a href="a">{{post.title}}</a></h2>     </header>
 
    <p>{{'post.on' | trans }} 
        <time datetime="{{ post.createdAt | date('c') }}">{{ post.createdAt | date }} </time> 
        {{ 'by' | trans }} <a href="a"> {{ post.author.name }} </a>
    </p>
</header>
 
<p> {{post.body |truncate(400)}} — <a href=""a">{{ 'read.more' | trans }} &raquo;</a></p>
</article>

C:\Bitnami\wampstack-5.4.38-0\sym_prog\myproject\src\Blog\ModelBundle\Entity\P ost.php

...
class Post extends Timestampable
{
    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;
 
    /**
     * @var string
     *
     * @ORM\Column(name="title", type="string", length=150)
     * @Assert\NotBlank
     */
    private $title;
 
    /**
     * @var string
     *
     * @ORM\Column(name="body", type="text")
     * @Assert\NotBlank
     */
    private $body;
 
    /**
     * @var Author
     *
     * @ORM\ManyToOne(targetEntity="Author", inversedBy="posts")
     * @ORM\JoinColumn(name="author_id", referencedColumnName="id", nullable=false)
     * @Assert\NotBlank
     */
    private $author;
...

C:\Bitnami\wampstack-5.4.38-0\sym_prog\myproject\src\Blog\ModelBundle\Entity\T imestampable.php

.... abstract class Timestampable
{
 
    /**
     *
     * @var \DateTime
     * @ORM\Column (name="created_at", type="datetime")
     */
    private $createdAt;
     /**
     * Construct
     */
    public function __construct()
    {
        $this->createdAt = new \DateTime();
    }....