在我的JSP页面中，对于ajax多部分表单数据提交，当未上传图像时，upload.parseRequest（request）返回空列表

Question

在我的.java 文件中，
 每当文件上传并通过ajax提交表单时， upload.parseRequest（request）会正确返回所有字段，

但是每当提交一个没有文件的表单时， upload.parseRequest（request）返回空列表。

有人可以建议我任何解决方法吗？

if (!isMultipart) {
System.out.println("Inside isMultipart ------------------------->" + imageName);                
} 
DiskFileItemFactory factory = new DiskFileItemFactory();

// Location to save data that is larger than maxMemSize.
factory.setRepository(new File(imagesavingLocation));

FileUpload upload = new ServletFileUpload(factory);
upload.setHeaderEncoding(request.getCharacterEncoding());
List items = null;

items = upload.parseRequest(request);
Iterator iterator = items.iterator ();

我的js文件如下所示

  var form = $('#merchantSignupForm')[0];

    var fd = new FormData(form);


    fd.append('firmname', $("#firmname").val());
    fd.append('firmtype', $("#firmtype").val());
    fd.append('pancard', $("#pancardnumber").val());
    fd.append('vatnumber', $("#vatnumber").val());
  fd.append('filevatnumber',$("input[name='filevatnumber']:checked").val());
    fd.append('contactnumber', $("#contactnumber").val());

    $.ajax({
      type: 'POST',
      async: false,
      enctype: 'multipart/form-data',
      url: urlCS+"?actionname=CustomerSupportAjaxHandler.setMerchantDetail&firmname="+$("#firmname").val(),
      data: fd,
      cache: false,
      processData: false,
      contentType: false,

      success: function(data){

          if(typeof data === "object" && data.status == 'success')
            {
                $("#merchantMsg").html("<span class='success_FieldText'>Merchant Sign up sucessfully</span>");
                 $('.realperson-text').click();
                  $(window).scrollTop($('#merchantMsg').offset().top);
                 $("#merchantSignupForm").get(0).reset(); 
            }
            else
            {   
                 $('.realperson-text').click();
                $('#captcha').val('Type the word*');
                $(window).scrollTop($('#merchantMsg').offset().top);
                $("#merchantMsg").html("<span class='errMsg'>  Error occured Please Try again ! </span>");
            }
      },
      error: function() 
        { 
             $('.realperson-text').click();
            $('#captcha').val('Type the word*');
            $(window).scrollTop($('#merchantMsg').offset().top);
            $("#merchantMsg").html("<span class='errMsg'>  Error occured Please Try again !</span>");
        }
    });