Feedburner issue

One of my client’s website had an issue where they cannot update the posts. I was assigned the task to debug and fix the issue. What I found out was that FeedBurner.php was causing the fatal error if $fb_urls are present or null.

here is the error

PHP Fatal error:  Uncaught Error: [] operator not supported for strings in /home/somewebsite/public_html/wp-content/plugins/a2-w3-total-cache/extensions/FeedBurner.php:28
Stack trace:
#0 /home/somewebsite/public_html/wp-includes/class-wp-hook.php(294): W3_FeedBurner->flush_feedburner(3952)
#1 /home/somewebsite/public_html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(true, Array)
#2 /home/somewebsite/public_html/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#3 /home/somewebsite/public_html/wp-includes/post.php(5047): do_action('publish_post', 3952, Object(WP_Post))
#4 /home/somewebsite/public_html/wp-includes/post.php(4284): wp_transition_post_status('publish', 'publish', Object(WP_Post))
#5 /home/somewebsite/public_html/wp-includes/post.php(4486): wp_insert_post(Array, false, true)
#6 /home/somewebsite/public_html/wp-admin/includes/post.php(419): wp_update_post(Array)
#7 /home/somewebsite/public_html/wp-admin/post.php(227): edit_post()

Here is the code before editing:

if ($fb_urls) 
            $fb_urls = explode("\n", $fb_urls);
$fb_urls[] = home_url();
            foreach($fb_urls as $url) {
                wp_remote_get('https://feedburner.google.com/fb/a/pingSubmit?bloglink=' . urlencode($url));
        }

Here is what I did to fix it

function flush_feedburner($post_id) {
        if (!w3_is_flushable_post($post_id, 'pgcache', $this->_config)) {
            return;
        }
        $fb_urls = w3tc_get_extension_config('feedburner','urls');
        
        if ($fb_urls) {
            $fb_urls = explode("\n", $fb_urls);
            $fb_urls[] = home_url();
            foreach($fb_urls as $url) {
                wp_remote_get('https://feedburner.google.com/fb/a/pingSubmit?bloglink=' . urlencode($url));
            }
        }
    }

Please update the feedburner.php file so that after any future update the issue should not occur again