Error: 'Trying to get property of non-object' - php

Question

So i'm having this trouble. Errors on lines 3,4,5. This is how i define object properties:
class Article {
//line 3
public $id; // line 4
public $pubDate; // line 5
public $title;
public $content;
And here is my method that gives an error:
public static function getById( $id ) {
$conn = new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD );
$sql = "SELECT *, UNIX_TIMESTAMP(pubDate) AS pubDate FROM material WHERE id = :id";
$st = $conn->prepare( $sql );
$st->bindValue( ":id", $id, PDO::PARAM_INT );
$st->execute();
$row = $st->fetch();
$conn = null;
if ( $row ) return new Article( $row );
}
I've tried to disable error by using:
error_reporting(0);
#ini_set('display_errors', 0);
But it's only masks the problem, publication still doe's not appear on page.
Thank you.
This is function constructor:
public function __construct($data = array()) {
if ( isset( $data['id'] ) ) $this->id = $data['id'];
if ( isset( $data['pubDate'] ) ) $this->pubDate = $data['pubDate'];
if ( isset( $data['title'] ) ) $this->title = $data['title'];
if ( isset( $data['content'] ) ) $this->content = $data['content'];
}
And function that calls getById method:
function viewArticle() {
if ( !isset( $_GET["articleId"] ) || !$_GET["articleId"] ) {
homepage();
return;
}
$results = array();
$results['article'] = Article::getById( (int) $_GET["articleId"] );
$results['pageTitle'] = $results['article']->title;
require( TEMPLATE_PATH . "/viewArticle.php" );
}

Answer 1

Solution has been found. Problem was - my stupidity.
Best regards for all who guided me and responded to my plea for help.