I'm working on a Wordpress template `content-article.php`

Here are the segment of my code:

```
$article_field[];
$article_field[] = 'test1';
$article_field[] = 'test2';
$article_field[] = 'test3';

echo $article_field[($page->ID + $page) % 3];

```

The PHP Notice: Trying to get property of non-object, is taking place at the line of `echo`

Even there's a warning, the script still execute fine and giving me correct result.

I'm rotating the `$article_field[]` element display based on pagination variable `$page`, where array index is calculated by current `page id` + `page number` % 3

How do I fix this PHP Notice?