JQuery Validation - require at least one field

JQuery Validation - require at least one field

Could anyone tell me why my form is still submitting if the user does not fill in any fields and clicks the search button???
  1.         <script language="javascript" type="text/javascript">
                $.validator.setDefaults({
                    submitHandler: function () { alert("Submitted"); }
                });

                $().ready(function () {

                    $.validator.addmethod("required_group", function (value, element) {
                        return $(element).find(".required_group:filled").length > 0;
                    }, "Please fill out at least one of these fields.");
                   
                    $.validator.addClassRules('required_group', {
                        'required_group': true
                    });

                    $('form').validate();
                });
            </script>