public static Attendee CreateAndAddAttendee(this Meeting meeting)
 {
     var atendee = new Attendee(Guid.NewGuid() + "*****@*****.**");
     meeting.AddAttendee(atendee);
     return atendee;
 }
 public static Attendee CreateAndAddAttendee(this Meeting meeting, string email)
 {
     var atendee = new Attendee(email);
     meeting.AddAttendee(atendee);
     return atendee;
 }
 public void AddAttendee(Attendee attendee)
 {
     if (isCanceled)
     {
         throw new MeetingCanceledException();
     }
     if (Attendies.Any(x => x.Email == attendee.Email))
     {
         return;
     }
     if (Attendies.Count >= MaximumNumberOfAttendies)
     {
         throw new NumberOfAttendiesExceeded();
     }
     Attendies.Add(attendee);
 }