Xcode 8 / Swift 3: "Expression of type UIViewController? is unused" warning : <p>I've got the following function which compiled cleanly previously but generates a warning with Xcode 8.</p>

<pre><code>func exitViewController()
{
    navigationController?.popViewController(animated: true)
}
</code></pre>

<blockquote>
  <p>"Expression of type "UIViewController?" is unused".</p>
</blockquote>

<p>Why is it saying this and is there a way to remove it?</p>

<p>The code executes as expected.</p>
