because the page is automatically submitted to the / apply processing page when the form is submitted, the JSON data
is returned, so the redirection is redirected to / applysuccess
using ajax. However, when the data is not submitted successfully, when you get the data, you see null
ask for help

//ajax
 $.ajax({
        type: "post",
        url: "/apply",
        async: true,
        dataType: "json",
        data: $("-sharpsub").serialize(),
        success: function (data) {

            $("-sharpsub").attr("method", "GET").attr("action", "/applysuccess");
            $("-sharpapply").html("<h3>" + data.message + "</h3>");
            $(".count").html(" " + data.count + " ");
        }
    });

< form action= "/ apply" method= "post" id= "sub" >

                <div class="form-group fl col-md-4">
                    <input class="form-control" name="first_name" placeholder="first name" required>
                    <input class="form-control" name="last_name" placeholder="last name" required>
                </div>
                <div class="form-group fl col-md-4">
                    <input class="form-control" name="position_id" placeholder="position id" required>
                    <input class="form-control" name="years_experience" placeholder="years experience" required>
                </div>
                <div class="form-group fl col-md-4">
                    <input class="form-control" name="expertise" placeholder="expertise" required>
                    <button id="applyBtn" type="submit" class="btn btn-primary btn-lg">Apply for Job NOW</button>
                </div>
            </form>