How can i fix this error

Hy,
i’m building a cinema website, i get an error if there is no content,

https://www.diviziatm.ro/1.jpg

In the website i get this if i have no content:

Warning: Invalid argument supplied for foreach() in /home/cinema/public_html/cinema/wp-content/themes/movies/tabfilm/detali-film.php on line 25

My code for display scenarist is under:

<span class="film"><b>Scenarist</b><br />
<?php foreach(get_field('scenaristi') as $post_object): ?>
<a class="arh-link" href="<?php echo get_permalink($post_object->ID); ?>">
<?php echo get_the_title($post_object->ID) ?></a><br /> <?php endforeach; ?>
</span>

For example: if i do not want to display something, i wish to apear the text: No actors.

Thanks. Excuse my english