Error when selecting nothing in listbox
<p>Hi I have a code that reads a text file and copies the content into a list box.
Everything is working fine, but when I click inside the listbox in a place where there is no item, a new error message appears and it points out that I have somthing wrong with this line:</p>

<pre><code>switch (listBox3.SelectedItem.ToString()) {
    case "Accessories":
        label4.Text = "None Required"; //Approval
        label13.Text = " "; //Approval
        label5.Text = "TTS";  //sent by
        label6.Text = "IT Co.";   //sender
        label7.Text = "2";  //urgent
        label8.Text = "3";  //normal
        label9.Text = "PC Name";   // required filed 1
        label10.Text = "PC Brand &amp;&amp; Model";  // required filed 2
        label11.Text = "B.C";  // required filed 3
        label12.Text = "Location";  // required filed 4
        label14.Text = "User Name";  // required filed 5
    break;
</code></pre>

<p>This just a piece of the code and the line which the compiler points out is this:</p>

<pre><code>switch (listBox3.SelectedItem.ToString())
</code></pre>

<p>How can I fix this issue?</p>
