title: Kohana image upload validation
body: <p>I'm having problems with image validation, documentation as always doesn't help, so there is my simple validation to check if image was uploaded</p>
  
  <pre><code>    $validate = Validation::factory($_FILES)
                  -&gt;rule('file', array('Upload::not_empty'));
  </code></pre>
  
  <p>But this gives me error 
  <code>ErrorException [ Warning ]: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members</code></p>
  
  <p>What could be causing this error?</p>