public void Maybe(string userId, string name, string message = null)
 {
     if (!_attendance.ContainsKey(userId))
     {
         _attendance[userId] = new AttendanceEntry(userId, name, AttendanceStatus.Maybe, message);
     }
     else
     {
         _attendance[userId].Maybe(message);
     }
 }
 public void In(string userId, string name)
 {
     if (!_attendance.ContainsKey(userId))
     {
         _attendance[userId] = new AttendanceEntry(userId, name, AttendanceStatus.Yes);
     }
     else
     {
         _attendance[userId].In();
     }
 }