PHImageManager.default().requestImage Error

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Hi, any idea why I am getting an error in line "21" ? 
	Thank you.

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1. final func chooseLastImage(_ sender: Any) {
2. 
3.     let imgManager = PHImageManager.default()
4. 
5.     let fetchOptions = PHFetchOptions()
6. 
7.     let requestOptions = PHImageRequestOptions()
8. 
9.     requestOptions.version = .original
10. 
11.     requestOptions.isSynchronous = false
12. 
13.     requestOptions.isNetworkAccessAllowed = false
14. 
15.     let targetSize: CGSize? = CGSize(width: photoImageView.bounds.width, height: photoImageView.bounds.height)
16. 
17.     fetchOptions.sortDescriptors = [NSSortDescriptor(key:"creationDate", ascending: true)]
18. 
19.     let fetchResult: PHFetchResult<PHAsset> = PHAsset.fetchAssets(with: .image, options: fetchOptions)
20. 
21.     imgManager.requestImage(for: fetchResult.lastObject!, targetSize: targetSize!, contentMode: .aspectFit, options: requestOptions) { (result, info) in
22. 
23.       guard let result = result else { return }
24. 
25.       DispatchQueue.main.async(execute: {
26. 
27.         self.pickedImage = result
28. 
29.         self.photoImageView.image = self.pickedImage
30. 
31.       })
32. 
33.     }
34. 
35.   }
36. 
37. extension PhotoViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {
38. 
39.   func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
40. 
41.     if let editedImage = info[UIImagePickerController.InfoKey.editedImage] as? UIImage {
42. 
43.         photoImageView.image = updatedImage
44. 
45.     } else if let image = info[UIImagePickerController.InfoKey.originalImage] as? UIImage {
46. 
47.       pickedImage = image
48. 
49.       photoImageView.image = pickedImage
50. 
51.     }
52. 
53.       dismiss(animated: true, completion: nil)
54. 
55.     }
56. 
57.     func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
58. 
59.       dismiss(animated: true, completion: nil)
60. 
61.   }
62. 
63. }

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