单元格中类型如下的单元格格式和公式时，有时候报空指针异常

点击文件名下载附件
双击G3或者G5 var numberCellType = new NumberCellType {DecimalPlaces = cellNode.DecimalPlaces, ReadOnly = false};
                    var cell = toSheet.Cells[2, 6];
                    cell.CellType = numberCellType;
                    cell.Formula = $E$3*100/$C$3;
错误如下所示：
ystem.Exception: Exception handled in FpSpread.WndProc ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at FarPoint.Win.Spread.CellType.GeneralEditor.set_ReadOnly(Boolean value)
   at FarPoint.Win.Spread.CellType.EditBaseCellType.set_ReadOnly(Boolean value)
   at FarPoint.Win.Spread.SpreadView.StartCellEditing(EventArgs e, Boolean formula)
   at FarPoint.Win.Spread.SpreadView.a(Int32 A_0, Int32 A_1, MouseEventArgs A_2)
   at FarPoint.Win.Spread.SpreadView.g(MouseEventArgs A_0)
   at FarPoint.Win.Spread.FpSpread.OnMouseDown(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at FarPoint.Win.Spread.FpSpread.WndProc(Message& m)
   --- End of inner exception stack trace ---
   at FarPoint.Win.Spread.FpSpread.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

---- Recent log messages:

---- Post-error application state information: