title: SWIFT ALAssetsLibrary not enumerating groups
body: <p>I'm trying to gather thumbnails of all the user's images into an array, but when I call the <code>enumerateAssetsUsingBlock</code> method of <code>ALAssetsLibrary</code> nothing seems to happen. </p>
  
  <pre><code>import UIKit
  import AssetsLibrary
  
  class ViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate  {
  
  
  @IBOutlet var photoLibView: UICollectionView
  var assetLibrary : ALAssetsLibrary = ALAssetsLibrary()
  
  
  func showCustomLibrary() {
      self.assetLibrary = ALAssetsLibrary()
  
      var assetsArray : [ALAsset] = []
      var imageArray : [CGImage] = []
      var count = 0
      var countOne = 0
      let assetsType : ALAssetsGroupType = Int(ALAssetsGroupAll)
  
      var groupBlock : ALAssetsLibraryGroupsEnumerationResultsBlock = {
  
          (group: ALAssetsGroup!, stop: UnsafePointer&lt;ObjCBool&gt;) in
          println("is goin")
          count++
          var assetBlock : ALAssetsGroupEnumerationResultsBlock = {
              (result: ALAsset!, index: Int, stop: UnsafePointer&lt;ObjCBool&gt;) in
              imageArray.append(result.thumbnail().takeRetainedValue())
              assetsArray.append(result)
              countOne++
          }
  
          group.enumerateAssetsUsingBlock(assetBlock)
  
  
      }
      var groupFailureBlock : ALAssetsLibraryAccessFailureBlock = {
          (NSError) in
          println("errorrrrrrrr")
  
      }
      assetLibrary.enumerateGroupsWithTypes(assetsType, usingBlock: groupBlock, failureBlock: groupFailureBlock)
  
  
  
      println("number of groups")
      println(count)
      println("number of total assets")
      println(countOne)
  
      self.photoLibView.insertItemsAtIndexPaths(imageArray)
  
  
  }
  
  
  }
  </code></pre>
  
  <p>When I run showCustomLibrary() is called, the compiler prints <code>number of groups
  0
  number of total assets
  0
  fatal error: unexpectedly found nil while unwrapping an Optional value
  </code>
  because it seems as though the groups of the <code>ALAssetsLibrary</code> are not being enumerated. ("is goin" is not being printed). Any idea what's going on here? Thanks in advance!</p>