toJson method
Implementation
core.Map<core.String, core.dynamic> toJson() => {
if (invoiceEndDate != null) 'invoiceEndDate': invoiceEndDate!,
if (invoiceStartDate != null) 'invoiceStartDate': invoiceStartDate!,
if (usageEndDateTime != null) 'usageEndDateTime': usageEndDateTime!,
if (usageStartDateTime != null)
'usageStartDateTime': usageStartDateTime!,
};