codice:
System.NullReferenceException: Riferimento a un oggetto non impostato su un'istanza di oggetto.   in System.Windows.Forms.DataGridViewCell.GetEditedFormattedValue(Object value, Int32 rowIndex, DataGridViewCellStyle& dataGridViewCellStyle, DataGridViewDataErrorContexts context)
   in System.Windows.Forms.DataGridViewCell.PaintWork(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts)
   in System.Windows.Forms.DataGridViewRow.PaintCells(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow, DataGridViewPaintParts paintParts)
   in System.Windows.Forms.DataGridViewRow.Paint(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow)
   in System.Windows.Forms.DataGridView.PaintRows(Graphics g, Rectangle boundingRect, Rectangle clipRect, Boolean singleHorizontalBorderAdded)
   in System.Windows.Forms.DataGridView.PaintGrid(Graphics g, Rectangle gridBounds, Rectangle clipRect, Boolean singleVerticalBorderAdded, Boolean singleHorizontalBorderAdded)
   in System.Windows.Forms.DataGridView.OnPaint(PaintEventArgs e)
   in System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
   in System.Windows.Forms.Control.WmPaint(Message& m)
   in System.Windows.Forms.Control.WndProc(Message& m)
   in System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)