gap property
Gap says why the fold did not happen or did not complete, when that is the case. An empty surface and an unreachable warehouse are different facts and a model must not report them as the same 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
String? gap;