unable to handle null values in ComboBox ?

Question

Hie friends

Well i used a button and combo box . when i click on button it should display what ever i selected in combo box :) when i select something in comboBox its working fine but when i un-intentionally click on button without selecting anything in comboBox ITS THROWING me Null Reference Exception :(

How to handle this ? Is there any other way except exceptional handling ?

My Code :
private void button1_Click(object sender, EventArgs e)
        {
                MessageBox.Show(comboBox1.SelectedItem.ToString());
        } 

                                        (OR)

private void button1_Click(object sender, EventArgs e)
        {
foreach(object obj in ComboBox1.SelectedItem.ToString())

MessageBox.Show(obj.ToString());
        } 

Foreach also failed to handle null but its not used here in this context :D
Thank you in advance