toJson method
Implementation
core.Map<core.String, core.dynamic> toJson() => {
if (issue != null) 'issue': issue!,
if (orderNumber != null) 'orderNumber': orderNumber!,
if (seriesBookType != null) 'seriesBookType': seriesBookType!,
if (seriesId != null) 'seriesId': seriesId!,
};