title: UIImage, check if contain image
body: <p>If I instantiate a UIImage like this :</p>
  
  <pre><code>UIImage *image = [[UIImage alloc] init];
  </code></pre>
  
  <p>The object is created but it doesn't contain any image.</p>
  
  <p>How I can check if my object contains an image or not?</p>