The solution is depending on CommonInterfaces.NETCoreLib.dll in develop branch

[BartVertongen]

This is just an interface to link UBL Documents with CII (CrossIndustry Invoices) documents.
So using this Interface UBL and CII documents have something in Common.

The Repositories CII and CommonInterfaces will be added later.

The Binaries are included so the code can still be used.