upstream property
Upstream credits the third-party work this project was published from — a free-text line, because the honest answer is a name and a title that no enum could hold. Absent means NOBODY HAS SAID, not that there is nothing to say.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? upstream;