title: Alert window after submiting FormPanel
body: <p>I have next problem... when i submit form and my Post method end. Form(or not)throwing empty alert window. how can I delete this throwing window?</p>
  
  <p><strong>ClienSide</strong></p>
  
  <pre><code> ....            
          final FormPanel form = new FormPanel();
          form.setAction(GWT.getModuleBaseURL()+"upload");
  
          form.setEncoding(FormPanel.ENCODING_MULTIPART);
          form.setMethod(FormPanel.METHOD_POST);
  
          VerticalPanel panel = new VerticalPanel();
          form.setWidget(panel);
  
          FileUpload upload = new FileUpload();
          upload.setName("uploadFormElement");
          panel.add(upload);
  
          fileButton.addClickHandler(new ClickHandler() {
              public void onClick(ClickEvent event) {
                  form.submit();
              }
          });
  </code></pre>
  
  <p><strong>FileUploadServlet</strong></p>
  
  <pre><code>public class FileUploadServlet extends HttpServlet {
  
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp)
              throws ServletException, IOException {
          super.doGet(req, resp);
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp)
              throws ServletException, IOException {
  
  
          if (ServletFileUpload.isMultipartContent(req)) {   
              FileItemFactory factory = new DiskFileItemFactory();
              ServletFileUpload upload = new ServletFileUpload(factory);
  
              try {
                  List&lt;FileItem&gt; items = upload.parseRequest(req);
                  for (FileItem fileItem : items) {
                      if (fileItem.isFormField()) continue;
                      String fileName = fileItem.getName();
                      if (fileName != null) {
                          fileName = FilenameUtils.getName(fileName);
                      }
                      File uploadedFile = new File("test.txt");
                      if (uploadedFile.createNewFile()) {
                          fileItem.write(uploadedFile);
                      }
  
                  }
              } catch (FileUploadException e) {
                  e.printStackTrace();
              } catch (Exception e) {
                  e.printStackTrace();
              }
          }
      }
  </code></pre>
  
  <p>Maybe someone knows the reason of this alert?</p>