public Task <IEnumerable <ValidationError> > Visit(UsageTrigger trigger)
{
var errors = new List <ValidationError>();
if (trigger.NumDays.HasValue && (trigger.NumDays < 1 || trigger.NumDays > 30))
{
errors.Add(new ValidationError(Not.Between("Num days", 1, 30), nameof(trigger.NumDays)));
}
return(Task.FromResult <IEnumerable <ValidationError> >(errors));
}