Date Formatting Returns Nil : <p>I'm getting nil when trying to create a date from a string. What am I doing wrong?</p>

<pre><code>let createdAt = passesDictionary["createdAt"] as? String
print(createdAt)
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let createdDate = dateFormatter.dateFromString(createdAt!)
print(createdDate)
</code></pre>

<p>createdAt is Optional("2016-05-03T19:17:00.434Z"), but createdDate is nil.</p>
