How to check if checkbox is checked in c# [duplicate]

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• What is a NullReferenceException, and how do I fix it? 32 answers

I'm trying to show a Message box on button clicked for the Checked Checkboxes in Datagridview

Here is my code:

private void btnSave_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < PayingDG.Rows.Count; i++)
        {
            if (PayingDG.Rows[i].Cells[4].Value.ToString() == "yes")//this is the checkbox column 
            {
                MessageBox.Show(i.ToString());
            }
        }
    }

It gives the following error:

Object reference not set to an instance of an object.

Any suggestions?