id property
ID is the link's handle, derived from its source and target — which is what makes re-declaring the same pair an update rather than a duplicate.
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? id;