inverse method
Inverses IsoDuration.
If IsoDuration is negative then it will be positive and vice versa.
Implementation
IsoDuration inverse() {
return IsoDuration(
years: years == 0 ? 0 : years.inverse(),
months: months == 0 ? 0 : months.inverse(),
weeks: weeks == 0 ? 0 : weeks.inverse(),
days: days == 0 ? 0 : days.inverse(),
hours: hours == 0 ? 0 : hours.inverse(),
minutes: minutes == 0 ? 0 : minutes.inverse(),
seconds: seconds == 0 ? 0 : seconds.inverse(),
);
}