After upgrading from 1.9.9 to ^2.x having "className" not found during the class mapping

[localpath]

ErrorException: Attempt to read property "className" on null

/var/www/giving/vendor/authorizenet/authorizenet/lib/net/authorize/api/contract/v1/ARBSubscriptionType.php:295
/var/www/giving/vendor/authorizenet/authorizenet/lib/net/authorize/api/controller/base/ApiOperationBase.php:138
/var/www/giving/vendor/authorizenet/authorizenet/lib/net/authorize/api/controller/base/ApiOperationBase.php:104
/var/www/giving/app/Subscription.php:393

The only thing I see different in our code for setting up ARB is we're passing the OrderType class with

$orderInfo = new AnetAPI\OrderType();
$orderInfo->setInvoiceNumber($details['id']);

Thanks for any insight. The rest of the SDK seems to work with how we we're using it.