Uncaught Error: Call to a member function asXML() on null

I have trouble when I try to export orders to XML file. Before the plugin worked perfectly for me.
I have not installed any new plugins or themes. (some may have updated)

This is error I get when I try to export any order.

<h2>Don't Panic</h2><p>The code you are trying to save produced a fatal error on line 2:</p><strong>Uncaught Error: Call to a member function asXML() on null in /data/web/virtuals/241238/virtual/www/wp-content/plugins/woo-order-export-lite/classes/core/class-wc-order-export-engine.php(366) : eval()'d code:2
Stack trace:
#0 /data/web/virtuals/241238/virtual/www/wp-content/plugins/woo-order-export-lite/classes/core/class-wc-order-export-engine.php(366): eval()
#1 /data/web/virtuals/241238/virtual/www/wp-content/plugins/woo-order-export-lite/classes/core/class-wc-order-export-engine.php(426): WC_Order_Export_Engine::validate_defaults(Array)
#2 /data/web/virtuals/241238/virtual/www/wp-content/plugins/woo-order-export-lite/classes/admin/tabs/ajax/trait-wc-order-export-admin-tab-abstract-ajax-export.php(22): WC_Order_Export_Engine::build_file(Array, 'estimate_previe...', 'file', 0, 0, 'test')
#3 /data/web/virtuals/241238/virtual/www/wp-content/plugins/woo-order-export-lite/classes/class-wc-order-export-admin.php(511): WC_Order_Export_Admin_Tab_Abstract->ajax_preview()
#4 /data/web/virtuals/241238/virtual/www/wp-includes/class-wp-hook.php(308): WC_Order_Export_Admin->ajax_gate('')
#5 /data/web/virtuals/241238/virtual/www/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters('', Array)
#6 /data/web/virtuals/241238/virtual/www/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#7 /data/web/virtuals/241238/virtual/www/wp-admin/admin-ajax.php(188): do_action('wp_ajax_order_e...')
#8 {main}
  thrown</strong>

What can I do to get plugin working again?

Many thanks

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