void IUtf8JsonSerializable.Write(Utf8JsonWriter writer)
 {
     writer.WriteStartObject();
     writer.WritePropertyName("frequencyInterval");
     writer.WriteNumberValue(FrequencyInterval);
     writer.WritePropertyName("frequencyUnit");
     writer.WriteStringValue(FrequencyUnit.ToSerialString());
     writer.WritePropertyName("keepAtLeastOneBackup");
     writer.WriteBooleanValue(KeepAtLeastOneBackup);
     writer.WritePropertyName("retentionPeriodInDays");
     writer.WriteNumberValue(RetentionPeriodInDays);
     if (Optional.IsDefined(StartOn))
     {
         writer.WritePropertyName("startTime");
         writer.WriteStringValue(StartOn.Value, "O");
     }
     writer.WriteEndObject();
 }