Error on Order with Refund

Hi,
When the shop admin makes a partial refund on an order, the following error is thrown (afterwards when the shop admin wants to view the order in detail view):

[30-Sep-2019 09:43:56 UTC] PHP Fatal error: Uncaught Error: Call to undefined method WPO\WC\PDF_Invoices\Documents\Bulk_Document::exists() in /var/www/vhosts/laks.com/httpdocs/wp-content/plugins/woocommerce-pdf-ips-pro/includes/wcpdf-pro-writepanels.php:110
Stack trace:
#0 /var/www/vhosts/laks.com/httpdocs/wp-includes/class-wp-hook.php(286): WPO\WC\PDF_Invoices_Pro\Writepanels->edit_numbers_dates(‘61276’)
#1 /var/www/vhosts/laks.com/httpdocs/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(”, Array)
#2 /var/www/vhosts/laks.com/httpdocs/wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#3 /var/www/vhosts/laks.com/httpdocs/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-admin.php(419): do_action(‘wpo_wcpdf_meta_…’, ‘61276’)
#4 /var/www/vhosts/laks.com/httpdocs/wp-admin/includes/template.php(1310): WPO\WC\PDF_Invoices\Admin->data_input_box_content(Object(WP_Post), Array)
#5 /var/www/vhosts/laks.com/httpdocs/wp-admin/edit-form-advanced.php(642): do_meta_boxes(Object(WP_Screen), ‘normal’, Object(WP_Post))
#6 in /var/www/vhosts/laks.com/httpdocs/wp-content/plugins/woocommerce-pdf-ips-pro/includes/wcpdf-pro-writepanels.php on line 110

Did we do anything wrong?
BR, George

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