title: Dictionary<AnyHashable: Any> where Any may hold nil value in Swift 3
body: <p>Can someone explain why this works in Swift 3?</p>
  
  <pre><code>var dict: [AnyHashable: Any]
  let b: AnyObject? = nil
  let c = b as Any
  
  dict = ["a": "aa", "b": c]
  </code></pre>
  
  <p>If I test</p>
  
  <p><code>dict["b"] == nil</code></p>
  
  <p>It returns false. Is it supposed to be right?</p>