Error when trying to make payment - Email is required if sending a receipt.

It seems that for receipts to work you must include the customer email in the transaction.

See - https://developer.paypal.com/braintree/articles/control-panel/transactio...
And - https://developer.paypal.com/braintree/docs/reference/request/transactio...

I have created a patch which seems to work.

This needs to be turned into a merge request so the tests can run.