title: Question Mark (?) after session variable reference - What does that mean
body: <p>I have had a code snippet comes to modify. In there i found this such syntax.</p>
  
  <pre><code>Session("LightBoxID")?.ToString()
  </code></pre>
  
  <p>I didn't understand what is that Question mark <strong>(?)</strong> there means. No googling helped me about any hint</p>