public Employee30(Employee30 other)
 {
     Name    = other.Name;
     Address = new Address30(other.Address);
 }
 public Employee30(string name, Address30 address)
 {
     Name    = name ?? throw new ArgumentNullException(paramName: nameof(name));
     Address = address ?? throw new ArgumentNullException(paramName: nameof(address));
 }