Next release

Fixed

Fix document reference elements being written in the wrong order, producing XML that fails UBL schema validation
- UBL declares these elements in an xsd:sequence, and the required order differs per document type
- On an Invoice, cac:ContractDocumentReference was written before cac:DespatchDocumentReference and cac:OriginatorDocumentReference after cac:AdditionalDocumentReference
- A CreditNote and a DebitNote inherit the same serializer but require a different order again
- Any document combining a contract reference with a despatch, receipt or additional reference was affected
Fix TypeError: Change setter types to nullable in reference classes to handle empty XML elements gracefully during parsing
- OrderReference::setId() now accepts ?string
- ProjectReference::setId() now accepts ?string
- ContractDocumentReference::setId() now accepts ?string
- InvoiceDocumentReference::setOriginalInvoiceId() now accepts ?string