title: how to add a empty string as default in the drop down where dropdown is a directive
body: <p>In my AngularJS project, I am having a dropdown field as a directive and the values are coming from the backend.The user can also leave the field without selecting the dropdown(optional field) but the problem is, there is no empty field from the backend. So I need to add an empty field into the dropdown as default.</p>
  
  <p>Since there is no option in the directive got struck in this issue.Googled a lot but didnt get any solutions yet.Kindly provide some suggestion.</p>
  
  <p>Note:Client machine,cant post the code.</p>