PHP Strict error on missing BIC

[naturefund-falk]

If you dont specify a bic for addTransfer/Directdebit, php throws a strict notice for missing debtorBic for file /lib/Digitick/Sepa/TransferFile/Facade/CustomerDirectDebitFacade.php on line 103.
The further processing of the missing bic seems ok, so this is only a minor issue.

Same would happen for all the other array fields.
https://github.com/digitick/php-sepa-xml/blob/master/lib/Digitick/Sepa/TransferFile/Facade/CustomerDirectDebitFacade.php#L77-L85