public void MergeGuests(Guest guest, Guest anonymousGuest)
{
if (!guest.OwnerId.HasValue)
{
throw new UserFriendlyException($"The guest with id = {guest.OwnerId} does not exist.");
}
if (anonymousGuest.OwnerId.HasValue)
{
throw new UserFriendlyException($"The guest with id = {anonymousGuest.OwnerId} is not anonymous.");
}
anonymousGuest.EditOwner(guest.OwnerId.Value);
}