title: reading optional chaining issue?
body: <p>I am getting the error:</p>
  
  <blockquote>
    <p>fatal error: unexpectedly found nil while unwrapping an Optional value. </p>
  </blockquote>
  
  <pre><code>DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {
      let imageString = self.thumblist1[indexPath.item]
      let imageUrl = URL(string: imageString)
      let imageData = try? Data(contentsOf: imageUrl!)
      DispatchQueue.main.async {
          if (imageData != nil)
          {
              cell2?.verticalImageView.image = UIImage(data: imageData!)
          }
      }
  }
  
  return cell2!
  </code></pre>