title: yii2 - Kartik file input - update
body: <p>This is the situation: I'm new on Yii2 and wanted to use some file uploader widget within ActiveForm.. so far I've found this excelent one: <a href="http://demos.krajee.com/widget-details/fileinput" rel="noreferrer">\kartik\widget\FileInput</a></p>
  
  <p>With this widget I can manage file upload and then, when enter in edit mode, show the previous uploaded image with the oportunite to replace it.</p>
  
  <p>The problem is that if I press the "Update" button of the form without modifying the image  yii says that the image "can't be empty" because I've set the 'required' rule in my model.</p>