Feature/despatch advice referenced document

[dbingham-tl]

Field BT-16 (DespatchAdviceReferencedDocument) was missing. According to XRechnung and ZUGFeRD Specifications the field is used to reference despatch advice numbers.
The Deutsche Bahn AG for example uses this in context of XRechnung to receive corresponding delivery-note numbers as there is no DeliveryNoteReferencedDocument in XRechnung.

[stephanstapel]

Thanks for your pull request!
Can you please initialize the property with an empty list.
Could you then make the setter internal and allow adding a document only via function? It's still barely noticeable in the code :) but I try to encapsulate those member variables more.
Is it also possible to add a test case?

[dbingham-tl]

Sure! I'll make the set of the Property internal. The wrapping Setter function already exists.
Regarding the list: According to the documentations there's only 0..1 allowed DespatchAdviceReferencedDocuments. Would a List still be correct here?

[stephanstapel]

Thanks again!
I didn't check the documentation :) If its 0..1, it shouldn't be a list but more a single object like here:

ZUGFeRD-csharp/ZUGFeRD/InvoiceDescriptor.cs

Line 68 in 86f6a6a

public DeliveryNoteReferencedDocument DeliveryNoteReferencedDocument { get; set; } = null;

[dbingham-tl]

There we go. I noticed that while creating the test, that "IssueDateTime" namespace in the Descriptor22Reader was never found in the saved xml, as the writer saves it under FormattedIssueDateTime.
Interestingly, there is not such problem with the DeliveryNoteReferencedDocument, but I simply copied the code from there (Reader & Writer).
The main difference I find is the WriteStartElement for the DeliveryNote part expluding the XRechnung profiles....But that should not change the namespace from FormattedIssueDateTime to IssueDateTime, right?

It's important to note: I only added the DateTime, as the format of DespatchAdviceReferencedDocument (According to specs) is a DocumentReference, which contains a date. However in the specs (including the examples) the date was never realy used.
Nevertheless, we support it with this merge :)