"System.NullReferenceException was unhandled" error after last valid row.

Hi, I'm using Visual Studio 2010 C#. I have a DataGridView on one of my Forms that is connected to SQL database table. That part works. I'm also using the dataGridView1_RowEnter Event to populate the selected information into different Textboxes as I scroll down the grid. That works until I get past the last row.

As soon as I go beyond the length of the table (past the last row) and enter the first NULL row, I get the following error.  

ERROR: >> System.NullReferenceException was unhandled

Why is the  "if (e.RowIndex >= 0)" logic statement not preventing the error and how do I solve this problem?

private void dataGridView1_RowEnter(object sender, DataGridViewCellEventArgs e)
        {
            DataGridViewRow row = this.dataGridView1.Rows[e.RowIndex];
            if (e.RowIndex >= 0)
            {                
                textBox1.Text = row.Cells[1].Value.ToString();
                textBox2.Text = row.Cells[2].Value.ToString();
                textBox3.Text = row.Cells[3].Value.ToString();
                textBox4.Text = row.Cells[4].Value.ToString();
            }