Version 7.x Fatal error from class-wp-filesystem-ftpext.php

Hi,

After upgrading to the latest 7.x, it seems something wrong with the plugin. Please refer to the following log, thank you.

Is it possible to disable PDF entirely since we do not attach PDF for customers (if that is the reason)?

PHP Fatal error:  Uncaught TypeError: ftp_nlist(): Argument #1 ($ftp) must be of type FTP\Connection, null given in /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php:438
Stack trace:
#0 /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php(438): ftp_nlist()
#1 /var/www/sampledomain.com/html/wp-content/plugins/woocommerce-delivery-notes/includes/services/class-pdf.php(70): WP_Filesystem_FTPext->exists()
#2 /var/www/sampledomain.com/html/wp-includes/class-wp-hook.php(341): Tyche\WCDN\Services\Pdf->init()
#3 /var/www/sampledomain.com/html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters()
#4 /var/www/sampledomain.com/html/wp-includes/plugin.php(522): WP_Hook->do_action()
#5 /var/www/sampledomain.com/html/wp-settings.php(771): do_action()
#6 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1374): require('...')
#7 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1293): WP_CLI\Runner->load_wordpress()
#8 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Bootstrap/LaunchRunner.php(28): WP_CLI\Runner->start()
#9 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/bootstrap.php(84): WP_CLI\Bootstrap\LaunchRunner->process()
#10 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/wp-cli.php(35): WP_CLI\bootstrap()
#11 phar:///usr/local/bin/wp/php/boot-phar.php(20): include('...')
#12 /usr/local/bin/wp(4): include('...')
#13 {main}
  thrown in /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php on line 438
Fatal error: Uncaught TypeError: ftp_nlist(): Argument #1 ($ftp) must be of type FTP\Connection, null given in /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php:438
Stack trace:
#0 /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php(438): ftp_nlist()
#1 /var/www/sampledomain.com/html/wp-content/plugins/woocommerce-delivery-notes/includes/services/class-pdf.php(70): WP_Filesystem_FTPext->exists()
#2 /var/www/sampledomain.com/html/wp-includes/class-wp-hook.php(341): Tyche\WCDN\Services\Pdf->init()
#3 /var/www/sampledomain.com/html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters()
#4 /var/www/sampledomain.com/html/wp-includes/plugin.php(522): WP_Hook->do_action()
#5 /var/www/sampledomain.com/html/wp-settings.php(771): do_action()
#6 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1374): require('...')
#7 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Runner.php(1293): WP_CLI\Runner->load_wordpress()
#8 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/WP_CLI/Bootstrap/LaunchRunner.php(28): WP_CLI\Runner->start()
#9 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/bootstrap.php(84): WP_CLI\Bootstrap\LaunchRunner->process()
#10 phar:///usr/local/bin/wp/vendor/wp-cli/wp-cli/php/wp-cli.php(35): WP_CLI\bootstrap()
#11 phar:///usr/local/bin/wp/php/boot-phar.php(20): include('...')
#12 /usr/local/bin/wp(4): include('...')
#13 {main}
  thrown in /var/www/sampledomain.com/html/wp-admin/includes/class-wp-filesystem-ftpext.php on line 438