Why appears in the work with UIGraphics?

Question

Swift

Good afternoon, I use this code to rotate images by a certain degree:

func rotated(degrees: CGFloat) -> UIImage? {
       let degreesToRadians: (CGFloat) -> CGFloat = { (degrees: CGFloat) in
         return degrees / 180.0 * CGFloat.pi
       }
       // Calculate the size of the rotated view's containing box for our drawing space
       let rotatedViewBox: UIView = UIView(frame: CGRect(origin: .zero, size: size))
       rotatedViewBox.transform = CGAffineTransform(rotationAngle: degreesToRadians(degrees))
       let rotatedSize: CGSize = rotatedViewBox.frame.size

       // Create the bitmap context
       UIGraphicsBeginImageContextWithOptions(rotatedSize, false, 0.0)

       guard let bitmap: CGContext = UIGraphicsGetCurrentContext(), let unwrappedCgImage: CGImage = cgImage else {
        fatalError("не фортануло1")
       }

       // Move the origin to the middle of the image so we will rotate and scale around the center.
       bitmap.translateBy(x: rotatedSize.width/2.0, y: rotatedSize.height/2.0)

       // Rotate the image context
       bitmap.rotate(by: degreesToRadians(degrees))

       bitmap.scaleBy(x: CGFloat(1.0), y: -1.0)

       let rect: CGRect = CGRect(
           x: -size.width/2,
           y: -size.height/2,
           width: size.width,
           height: size.height)

       bitmap.draw(unwrappedCgImage, in: rect)

      let newImage = UIGraphicsGetImageFromCurrentImageContext()!

       UIGraphicsEndImageContext()
            return newImage
       
     }

And sometimes there is an error in this line

let newImage = UIGraphicsGetImageFromCurrentImageContext()!

as if UIGraphicsGetImageFromCurrentImageContext = nil. But this does not always happen, if I restart the program, then everything is ok. Tell me, what could be the reasons? Can problems with streams?