[2005] Problem with printing

I tried this code to print from datagridview but it show me error at this line in line += cell.Value.ToString
the eroro
Object reference not set to an instance of an object.
How to fix this problem

vb Code:

Private Sub Button1_Click
 Dim PrintDoc As New PrintDocument
        AddHandler PrintDoc.PrintPage, AddressOf Me.PrintDGV
        PrintDoc.Print()
End Sub

vb Code:

Private Sub PrintDGV(ByVal sender As Object, _
  ByVal ev As PrintPageEventArgs)
        Dim line As String
        For Each row As DataGridViewRow In DataGridView1.Rows
            line = String.Empty
            For Each cell As DataGridViewCell In row.Cells
                line += cell.Value.ToString
            Next
            ' Render line to printer here
            Dim printFont As New System.Drawing.Font("Arial", 15, System.Drawing.FontStyle.Regular)
            Dim y As Integer
            y += 20
            ev.Graphics.DrawString(line, printFont, System.Drawing.Brushes.Black, 10, y)
        Next
    End Sub

How many references are there on that line? There are three, so it really can't be that hard to work out. There's 'line', which we know is not Nothing because you assigned it a value two lines before. There's cell, which we know is not Nothing because you assigned it a value one line before. The only other option is cell.Value. If there's no Value in the cell then you can't call ToString on it. An object that doesn't exist doesn't have a ToString method.

I tried this without ToString " line += cell.Value" and it succeed with me.
I want to print with column headeres and with lines of column?

Merrion has posted a submission in the VB.NET CodeBank forum that does all the heavy lifting when printing a grid.