Why is the image get deleted when updating in MVC

See more:

file

MVC4

MVC5

I am doing a project in that I am adding an image and a text.I have given an image and text and that works perfectly. but when I change the text only the image got deleted and only the text seems to appear.

controller

public async Task<ActionResult> StudentList(Student student, HttpPostedFileBase Img)
       {
           if (Img != null)
           {
               var imageTypes = new string[]{
                                  "image/gif",
                                  "image/jpeg",
                                  "image/pjpeg",
                                  "image/png"
                               };
               if (Img.FileName == null || Img.ContentLength == 0)
               {
                   ModelState.AddModelError("Images", "This field is required");
               }
               else if (!imageTypes.Contains(Img.ContentType))
               {
                   ModelState.AddModelError("Images", "Please choose either GIF, JPG or PNG image.");
               }
               if (ModelState.IsValid)
               {
                   if (Img != null)
                   {
                       var fileName = Path.GetFileName(Img.FileName);
                       var directoryToSave = Server.MapPath(Url.Content("~/Images"));
                       var pathToSave = Path.Combine(directoryToSave, fileName);
                       Img.SaveAs(pathToSave);
                       student.Images = fileName;
                   }
                   db.Entry(student).State = EntityState.Modified;
                   await db.SaveChangesAsync();
                   return RedirectToAction("StudentList", "Students", new { @id = 2 });
               }
           }
           else
           {
               if(ModelState.IsValid)
               {
                   db.Entry(student).State = EntityState.Modified;
                   await db.SaveChangesAsync();
                   return RedirectToAction("StudentList", "Students", new { @id = 2 });
               }
           }
           return View(student);
       }

view

<div class="form-group">
            @Html.LabelFor(model => model.Images, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                <div class="editor-field">
                    @Html.DisplayTextFor(model => model.Images)
                    @Html.TextBoxFor(m => m.Images, new { type = "file" })
                </div>
            </div>
            @Html.ValidationMessageFor(model => model.Images, "", new { @class = "text-danger" })
        </div>

I don't know why this happends, when I just click the save button the image get deleted. In the

@Html.DisplayTextFor(model => model.Images)

field it will get the image name but it is not passing to the httpPost method StudentList action method. why is this happening ?? how can I change text without deleting image??
can anyone please help me to find the solution ?

What I have tried:

Have searched many times but can't fix this error.