isAfter method Null safety

Returns true if this occurs after other.

The comparison is independent of whether the time is in UTC or in the local time zone.

var now = DateTime.now();
var later = now.add(const Duration(seconds: 5));
assert(later.isAfter(now));
assert(!now.isBefore(now));

// This relation stays the same, even when changing timezones.
assert(later.isAfter(now.toUtc()));
assert(later.toUtc().isAfter(now));

assert(!now.toUtc().isBefore(now));
assert(!now.isBefore(now.toUtc()));