Undefined array key message

After upgrading to the new alpha3, I always get these PHP notices:

Undefined array key "billing_information" in Drupal\commerce_shipping_same_as_billing\Plugin\Commerce\CheckoutPane\PaymentInformation->validatePaneForm() (line 37 of modules/commerce_shipping_same_as_billing/src/Plugin/Commerce/CheckoutPane/PaymentInformation.php).

Warning: Trying to access array offset on null in Drupal\commerce_shipping_same_as_billing\Plugin\Commerce\CheckoutPane\PaymentInformation->validatePaneForm() (line 37 of modules/commerce_shipping_same_as_billing/src/Plugin/Commerce/CheckoutPane/PaymentInformation.php).

The module seems to work fine otherwise...