title: Value of optional type 'UIImage?' not unwrapped
body: <p>I'm trying to create a simple filter app that filters the displayed image upon a button press.</p>
  
  <pre><code> @IBAction func applyFilter(sender: AnyObject) {
  
      // Create an image to filter
      let inputImage = CIImage(image: photoImageView.image)
  
      // Create a random color to pass to a filter
      let randomColor = [kCIInputAngleKey: (Double(arc4random_uniform(314)) / 100)]
  
      // Apply a filter to the image
      let filteredImage = inputImage.imageByApplyingFilter("CIHueAdjust", withInputParameters: randomColor)
  
      // Render the filtered image
      let renderedImage = context.createCGImage(filteredImage, fromRect: filteredImage.extent())
  
      // Reflect the change back in the interface
      photoImageView.image = UIImage(CGImage: renderedImage)
  
  }
  </code></pre>
  
  <p>I keep getting the error: </p>
  
  <blockquote>
    <p>Value of optional type 'UIImage?' not unwrapped.</p>
  </blockquote>
  
  <p>What am I doing wrong here? I'm a Swift beginner.</p>