title: Is there a way to store an array of optionals in NSCache?
body: <p>I can't for the life of me figure out how to store anything to do with an optional in NSCache. I can understand directly storing an optional would not make sense, but storing an array or dictionary where some options may be optional certainly seems like it should be possible.</p>
  
  <p>Yet a simple example doesn't work:</p>
  
  <pre><code>let dict: [String: String?] = ["foo": "bar"]
  NSCache().setObject(dict, forKey: "dict")
  </code></pre>
  
  <p>Is there something I'm overlooking or is there really no way to do this?</p>