public Address(int id, ExternalAgent agent, AddressVO addressDetails)
            : this()
        {
            if (agent == null)
            {
                throw new ArgumentNullException("External agent is required.");
            }

            Id             = id;
            Agent          = agent;
            AddressDetails = addressDetails;
        }
        public ContactPerson(int id, ExternalAgent agent, PersonName name, PhoneNumber telephone, string notes)
            : this()
        {
            if (agent == null)
            {
                throw new ArgumentNullException("External agent is required.");
            }

            Id          = id;
            Agent       = agent;
            ContactName = name;
            Telephone   = telephone;
            Notes       = notes;

            CheckValidity();
        }