title: Argument type error on MKPlacemark
body: <p>I'm trying to write in swift a function that create a MKMapItem but I get a String error. Here is the code:</p>
  
  <pre><code>func mapItem() -&gt; MKMapItem {
      let addressDictionary = [String(kABPersonAddressStreetKey): subtitle]
      let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDictionary)
  
      let mapItem = MKMapItem(placemark: placemark)
      mapItem.name = title
  
      return mapItem
  }
  </code></pre>
  
  <p>I got the following error when I try to create <code>placemark</code>: </p>
  
  <blockquote>
    <p>Cannot convert value of type "[String : String?]" to expected argument type "[String : AnyObject]?</p>
  </blockquote>
  
  <p>Full class code :</p>
  
  <pre><code>class Bar: NSObject, MKAnnotation {
  
      // MARK: Properties
      let id: Int
      let title: String
      let locationName: String
      let url: String
      let imageUrl: String
      let tags: String
      let coordinate: CLLocationCoordinate2D
  
      // MARK: Initialisation
      init(id: Int, adress: String, name: String, url: String, tags: String, imageUrl: String, coordinate: CLLocationCoordinate2D) {
          // Affectation des attributs
          self.id = id
          self.title = name
          self.locationName = adress
          self.url = url
          self.imageUrl = imageUrl
          self.tags = tags
          self.coordinate = coordinate
      }
  
      // MARK: Subtitle
  
      var subtitle: String {
          return locationName
      }
  
      // MARK: Helper
  
      func mapItem() -&gt; MKMapItem {
          var addressDictionary : [String:String]?
          addressDictionary = [String(kABPersonAddressStreetKey): subtitle]
  
          let placemark = MKPlacemark(coordinate: coordinate, addressDictionary: addressDictionary)
  
          let mapItem = MKMapItem(placemark: placemark)
          mapItem.name = title
  
          return mapItem
      }    
  }
  </code></pre>