title: Vaadin 7 : java.lang.IllegalStateException: Push is not available
body: <p>Why i'm getting this error : </p>
  
  <pre><code> javax.servlet.ServletException: com.vaadin.server.ServiceException: java.lang.IllegalStateException: Push is not available. See previous log messages for more information.
  com.vaadin.server.VaadinServlet.service(VaadinServlet.java:240)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
  </code></pre>
  
  <p>When i'm using the Push annotation :</p>
  
  <pre><code>@Push(PushMode.MANUAL)
  public class KopivaadincomponentsUI extends UI {
  
  @Override
  protected void init(VaadinRequest request) {...
  
     }
  }
  </code></pre>