How to make file uploading optional using Mvc 4 - asp.net-mvc

Question

I am uploading 3 types of files, i.e 1)video 2)image 3)document.
if i am uploading all three files at once so it is upload and show successfully, but if i want to skip one the file of uploading then it giving me following errors. Please Help me here:
httpPostedFile.SaveAs(fileSavePath);
db.SaveChanges();
one the errors is because of sending path to db i guess.
[HttpPost]
public ActionResult AddSKU(SKU_Det skufiles, IEnumerable<HttpPostedFileBase> files)
{
var httpPostedFile = Request.Files[0];
if (httpPostedFile != null)
{
var uploadFilesDir = System.Web.HttpContext.Current.Server.MapPath("~/Content/Videos");
if (!Directory.Exists(uploadFilesDir))
{
Directory.CreateDirectory(uploadFilesDir);
}
var fileSavePath = Path.Combine(uploadFilesDir, httpPostedFile.FileName);
httpPostedFile.SaveAs(fileSavePath);
}
foreach (var file in files)
{
if (file != null && file.ContentLength > 0)
{
file.SaveAs(HttpContext.Server.MapPath("~/Areas/Admin/Images/") + file.FileName);
}
}
SKU_Det sku = new SKU_Det();
sku.SKU = skufiles.SKU;
sku.VideoPath = Request.Files[0].FileName;
sku.Imagepath = sku.FilePath = Request.Files[1].FileName;
sku.FilePath = sku.FilePath = Request.Files[2].FileName;
db.SKU_Det.Add(sku);
db.SaveChanges();