public void OnBoardRemoved(Board board)
 {
     if (BoardRemoved != null)
     {
         BoardRemoved.Invoke(board, null);
     }
 }
        /// <summary>
        /// Delete exchange board.
        /// </summary>
        /// <param name="board">Exchange board.</param>
        public virtual void Delete(ExchangeBoard board)
        {
            if (board == null)
            {
                throw new ArgumentNullException(nameof(board));
            }

            _boards.Remove(board.Code);
            BoardRemoved?.Invoke(board);
        }