Object reference not set to an instance of an object.

public class Files
   {
       [Key]
       public int DocumentId { get; set; }
       public string Name { get; set; }
       public string FileType { get; set; }
      public byte[] DataFiles { get; set; }

<pre>public class DemoController : Controller
    {
        private readonly ApplicationDbContext _context;
        public DemoController(ApplicationDbContext context)
        {
            _context = context;
        }
        public IActionResult Index()
        {
            var result = _context.Files.ToList();
            return View(result);
        }

        [HttpPost]
        public IActionResult Index(IFormFile files)
        {
            if (files != null)
            {
                if (files.Length > 0)
                {
                    //Getting FileName
                    var fileName = Path.GetFileName(files.FileName);
                    //Getting file Extension
                    var fileExtension = Path.GetExtension(fileName);
                    // concatenating  FileName + FileExtension
                    var newFileName = String.Concat(Convert.ToString(Guid.NewGuid()), fileExtension);

                    var objfiles = new Files()
                    {
                        DocumentId = 0,
                        Name = newFileName,
                        FileType = fileExtension,
                    };

                    using (var target = new MemoryStream())
                    {
                        files.CopyTo(target);
                        objfiles.DataFiles = target.ToArray();
                    }

                    _context.Files.Add(objfiles);
                    _context.SaveChanges();

                }
            }
            return View();
        }

           public IActionResult DownloadImage(int id)
       {
           byte[] bytes;
         string fileName, contentType;
        var item = _context.Files.FirstOrDefault(c => c.DocumentId == id);

             if (item != null)
          {
                   fileName = item.Name;

                  contentType = item.FileType;
                  bytes = item.DataFiles;
                  return File(bytes, contentType, fileName);
               }
             return Ok("Can't find the File");
            }      
    }
}

<pre>@model List<Info.Models.Files>
@{
    ViewData["Title"] = "Index";
}

<h1>Index</h1>
<div class="row">
    <div class="col-md-5">
        <form method="post" enctype="multipart/form-data" asp-controller="Demo" asp-action="Index">
            <div class="form-group">
                <div class="col-md-10">
                    <p>Upload file</p>
                    <input class="form-control" name="files" type="file" />
                </div>
            </div>
            <div class="form-group">
                <div class="col-md-10">
                    <input class="btn btn-success" type="submit" value="Upload" />
                </div>
            </div>
        </form>
    </div>
</div>
<ul>
    @foreach (var item in Model)
    {
        <li>
            <a asp-action="DownloadImage"
               asp-route-filename="@item.Name">
                @item.Name
            </a>
        </li>
    }
</ul>