public static IRuleBuilderOptions <T, string> DateValidation <T>(this IRuleBuilder <T, string> rule)
{
return(rule
.NotEmpty()
.WithMessage("Order date cannot be empty.")
.MustAsync(async(orderDate, cancellation) => await ValidationHelpers.BeValidDateFormat(orderDate))
.WithMessage("Order date must be of format: d.MM.yyyy e.g. 12.02.2012"));
}