title: Swift: unexpectedly found nil while unwrapping an Optional value
body: <pre><code>var session = NSUserDefaults.standardUserDefaults().stringForKey("session")!
  println(session)
  </code></pre>
  
  <p>I am getting crash with following error:</p>
  
  <p>fatal error: unexpectedly found nil while unwrapping an Optional value</p>