Cannot perform runtime binding on a null reference ViewBag.Message

Why I got this error with ViewBag.Message

"Cannot perform runtime binding on a null reference"

This is the controller code :

 public ActionResult Edit(List<RESULT> list)
        {
           
            if (ModelState.IsValid)
            {
                using (db_a85fa6_globalqualityEntities db = new db_a85fa6_globalqualityEntities())
                {
                    foreach (var i in list)
                    {
                        var c = db.RESULTS.Where(a => a.ID.Equals(i.ID)).FirstOrDefault();
                        if (c != null)
                        {
                            c.RESULT1 = i.RESULT1;
                        }
                    }
                    db.SaveChanges();
                    //return RedirectToAction("Details");

                }
                ViewBag.Message("Updated Successfully");
                return View(list);
                
            }
            else
            {
                ViewBag.Message("Failed ! Please try again");
                return View(list);
            }
          

        }

This is view code :

  <div class="form-group">
            <div class="col-md-offset-2 col-md-10" style="margin:100px;">
                <input type="submit" value="Save" class="btn btn-danger" />
               </div>
        </div>

    if (ViewBag.Message != null)
    {
        <p style="color:green;font-size:16px;">
            @ViewBag.Message
        </p>
    }

when click SAVE button its not show the message and show the error on this line of code :

 ViewBag.Message("Updated Successfully");

How to solve it ?