         containerView.addSubview(tempImage)
         
         if transitionMode == .present {
-            transitionInfo.fromView!.alpha = 0
+            transitionInfo.fromView?.alpha = 0
             let imageViewer = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as! GSImageViewerController
                 imageViewer.view.layoutIfNeeded()
             

        self.fromView = fromView
    }
    
    weak var fromView : UIView?
    
    fileprivate var convertedRect : CGRect?

                completion: { _ in
                    tempMask.removeFromSuperview()
                    imageViewer.view.removeFromSuperview()
                    self.transitionInfo.fromView?.alpha = 1
                    transitionContext.completeTransition(true)
                }
            )
