Error when creating a user account

Hi!

In our shop, users can register without ordering something. If the DHL plugin is active, this user registration fails with the follwoing error:

Fatal error: Uncaught Error: Call to a member function get_id() on null in /xxx/htdocs/xxx/wp-content/plugins/dhl-for-woocommerce/includes/abstract-pr-dhl-wc-order.php:381
Stack trace: #0 /xxx/htdocs/xxx/wp-includes/class-wp-hook.php(287): PR_DHL_WC_Order->add_tracking_note_email_placeholder()
#1 /xxx/htdocs/xxx/wp-includes/plugin.php(206): WP_Hook->apply_filters()
#2 /xxx/htdocs/xxx/wp-content/plugins/woocommerce/includes/emails/class-wc-email.php(310): apply_filters()
#3 /xxx/htdocs/xxx/wp-content/plugins/woocommerce/includes/emails/class-wc-email.php(390): WC_Email->format_string()
#4 /xxx/htdocs/xxx/wp-content/plugins/woocommerce-german-market/inc/WGM_Email_Double_Opt_In_Customer_Registration.php(116): WC_Email->get_heading()
#5 /xxx/htdocs/xxx/wp-content/plugins/woocommerce/includes/emails/class-wc-email.php(54 in /mnt/web419/a3/17/5694017/htdocs/WordPress_03/wp-content/plugins/dhl-for-woocommerce/includes/abstract-pr-dhl-wc-order.php on line 381

If the DHL plugin is disabled, everything works as expected.

Any help is appreciated.

Thanks,
Marc

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