// Constructor:
protected Customer(
string address, int yearsOfUsage, Tariff tariff)
{
if (string.IsNullOrEmpty(address))
{
throw new ArgumentNullException(nameof(address));
}
if (yearsOfUsage < 0)
{
throw new ArgumentOutOfRangeException(nameof(yearsOfUsage));
}
Address = address;
YearsOfUsage = yearsOfUsage;
Tariff = tariff;
}