         self.layer.addSublayer(shapeLayer);
         
         displayLink = CADisplayLink(target: self, selector: #selector(NumberMorphView.updateAnimationFrame));
-        displayLink.frameInterval = 1;
-        displayLink.paused = true;
-        displayLink.addToRunLoop(NSRunLoop.currentRunLoop(), forMode: NSRunLoopCommonModes);
+        displayLink?.frameInterval = 1;
+        displayLink?.paused = true;
+        displayLink?.addToRunLoop(NSRunLoop.currentRunLoop(), forMode: NSRunLoopCommonModes);
         
         endpoints_original[0] = [[500, 800], [740, 400], [500, 0],   [260, 400], [500, 800]];
         endpoints_original[1] = [[383, 712], [500, 800], [500, 0],   [500, 800], [383, 712]];

        if currentFrame > maxFrames {
            currentFrame = 1;
            currentDigit = _nextDigit;
            displayLink.paused = true;
            drawDigitWithoutAnimation(currentDigit);
        }
    }

}

// Recommended ration for width : height is 13 : 24
@IBDesignable public class NumberMorphView: UIView {
    
    private static let DEFAULT_FONT_SIZE: CGFloat = 24;
    
