/// <summary>
 /// Indexer for the comments collection
 /// </summary>
 /// <param name="cell">The cell</param>
 /// <returns>The comment</returns>
 public ExcelComment this[ExcelCellAddress cell]
 {
     get
     {
         ulong cellID = ExcelCellBase.GetCellID(Worksheet.SheetID, cell.Row, cell.Column);
         if (_comments.IndexOf(cellID) >= 0)
         {
             return(_comments[cellID] as ExcelComment);
         }
         else
         {
             return(null);
         }
     }
 }
 /// <summary>
 /// Indexer for the comments collection
 /// </summary>
 /// <param name="cell">The cell</param>
 /// <returns>The comment</returns>
 public ExcelComment this[ExcelCellAddress cell]
 {
     get
     {
         ulong cellID=ExcelCellBase.GetCellID(Worksheet.SheetID, cell.Row, cell.Column);
         if (_comments.IndexOf(cellID) >= 0)
         {
             return _comments[cellID] as ExcelComment;
         }
         else
         {
             return null;
         }
     }
 }