Code with problems after PHP update from 7.4 to 8.1

This code was working fine with PHP 7.4:

(...)
@update_post_meta($post->ID, 'discount-extra-site', array_map( 'strip_tags', $_POST['discount-extra-site'] ) );
    (...)
    <option value="<?php the_ID(); ?>" <?php if (is_array($sites_discounted) && in_array(get_the_ID(), $sites_discounted)) { echo "selected"; } ?>><?php the_title(); ?></option>
(...)

Code (markup):

But the update_post_meta is not working so well after upgrade to PHP 8.1

I mean, it saves if I add some data, but if I want to remove it don't let me...
I can change and add more data, but don't let me remove it completely.

It gives me the following error:

The line 963 is:

(...)
@update_post_meta($post->ID, 'discount-extra-site', array_map( 'strip_tags', $_POST['discount-extra-site'] ) );
(...)

Code (markup):

Any idea how to fix this, please?

Thank you in advance

 

Well, it reports that the

$_POST['discount-extra-site']

Code (markup):

is null - are you sure it is actually containing anything? And is an array?

 

Thank you for helping me, PoPSiCLe!

I tried to use the chatgpt to solve this and the AI gave me this code that really worked, but it seems too big!
Do I need the entire code to make this work?

if (isset($_POST['discount-extra-site'])) {
$discount_extra_site = $_POST['discount-extra-site'];

// Check if $_POST['discount-extra-site'] is an array and not empty
if (is_array($discount_extra_site) && !empty($discount_extra_site)) {
// Use array_map only if $_POST['discount-extra-site'] is an array and not empty
$sanitized_discount_extra_site = array_map('strip_tags', $discount_extra_site);

// Update post meta with the sanitized array
update_post_meta($post->ID, 'discount-extra-site', $sanitized_discount_extra_site);
} else {
// If the array is null or empty, remove the post meta
delete_post_meta($post->ID, 'discount-extra-site');
}
} else {
// If $_POST['discount-extra-site'] is not set, remove the post meta
delete_post_meta($post->ID, 'discount-extra-site');
}

Code (markup):