PHP Warning when accessing invalid subscription links with missing post ID

Hi there,

I’ve identified a reproducible PHP warning in the current version of the Subscribe to Comments Reloaded plugin, specifically when handling subscription links for posts that no longer exist.

The issue:

When a user tries to manage their subscription using a link that includes an invalid or deleted post ID via the srp parameter (e.g., after a site rebuild or content cleanup), the following PHP warnings are thrown:

PHP Warning:  Trying to access array offset on value of type null in wp_subscribe_reloaded.php on line 1780
PHP Warning:  Attempt to read property "post_content" on null in wp_subscribe_reloaded.php on line 1780

How to reproduce:

1. Visit a link like this (valid structure, but invalid post ID):

https://yoursite.com/gerir-subscricoes/?srp=123456&srk=xyz&sra=s&srsrc=f

If the post ID (srp) doesn’t correspond to an existing post, the plugin tries to access $data[0]->post_content even though $data is null.

Root cause:

The method management_page_sc() assumes that $this->subscribe_reloaded_manage() will always return a valid array containing post data. But if the post ID is invalid or deleted, the return is null, and trying to access [0]->post_content causes the warning.

Suggested fix:

Inside the management_page_sc() function (around line 1780), consider adding a safety check like:

public function management_page_sc() {
    $data = $this->subscribe_reloaded_manage();

    if ( isset($data[0]) && isset($data[0]->post_content) ) {
        return $data[0]->post_content;
    }

    return '<p>' . __( 'The subscription link is not valid or the original post has been removed.', 'subscribe-to-comments-reloaded' ) . '</p>';
}

This will prevent the PHP warnings and provide a better user experience in the case of outdated or broken subscription links.

Thanks for your great work on this plugin — I hope this helps make it even more robust in future versions!

Best regards,
Ângelo Antunes