错误：对象引用未设置为对象的实例。关于datagridview到csv export的vb.net

Question

美好的一天，

我正在运行下面的代码将DatagridView1保存为csv格式，但是rowcontents.Add（c.Value.ToString（））正在提升未设置为对象实例的Object引用。错误......不知道该怎么做......

Using sw As New IO.StreamWriter(path)
        Dim rowcontents As New List(Of String)
        For Each col As DataGridViewColumn In DataGridView1.Columns
            rowcontents.Add(col.HeaderText)
        Next
        sw.WriteLine(String.Join(",", rowcontents))
        For Each r As DataGridViewRow In DataGridView1.Rows
            rowcontents.Clear()
            For Each c As DataGridViewCell In r.Cells
                rowcontents.Add(c.Value.ToString())
            Next
            sw.WriteLine(String.Join(",", rowcontents))
        Next
    End Using