existing property
Existing reports that the fork was already there. GitHub answers 202 either way, so without this a caller cannot tell "made you one" from "you had one".
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
bool? existing;