Getting comboBox1.SelectedValue

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        switchItem();
    }
private void switchItem()
        {
            var content = richTextBox1;
            switch (comboBox1.SelectedValue.ToString())
            {
                case "Fruit":
                    content.Text = "Apple";
                    break;
                default:
                    content.Rtf = "Not Selected";
                    break;
            }
        }

As you can see, I'm trying to get the SelectedValue of comboBox1 and this object reference not set to an instance of an object error showed up. What should I do?