toJson method
Implementation
core.Map<core.String, core.dynamic> toJson() => {
if (endTime != null) 'endTime': endTime!,
if (graceEndTime != null) 'graceEndTime': graceEndTime!,
if (startTime != null) 'startTime': startTime!,
if (upgradeTime != null) 'upgradeTime': upgradeTime!,
};