Unable to use BulkPaymentAuthorisationRequest and BulkPaymentRequest methods

[matteo-mohara]

The methods required to create a bulk payment fail with the following error:

Invalid value for 'currency', must not be None

The error is due to the response's amount object not including a currency field and thus causing the deserialisation to fail.
The issue can be circumvented by returning the raw response before deserialisation from api_client.py