how to upload multi image in mvc4?

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MVC4

how to insert multi image here is my code but object reference error occur
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public ActionResult ProductSetup(IEnumerable<httppostedfilebase> files)
{
using (EcomShopingEntities Entities = new EcomShopingEntities())
{
ProImage_Shoping obj ;

Guid nimgGUID;

foreach (var file in files)
{
nimgGUID = Guid.NewGuid();
obj = new ProImage_Shoping();
obj.ProductId = 1;

if (!file.FileName.Trim().Equals(""))
{
string strExt = Path.GetExtension(file.FileName);

if (strExt.ToLower() == ".gif" || strExt.ToLower() == ".jpg" || strExt.ToLower() == ".png" || strExt.ToLower() == ".jpeg")
{
string ImgPath = Server.MapPath(ConfigurationManager.AppSettings.Get("product"));

ImgPath = ImgPath + "\\";

if (!System.IO.Directory.Exists(ImgPath))
{
System.IO.Directory.CreateDirectory(ImgPath);
}

ImgPath = ImgPath + "\\" + nimgGUID.ToString().Trim() + file.FileName.Substring(file.FileName.LastIndexOf('.')).ToLower();
file.SaveAs(ImgPath);
obj.ImageName = nimgGUID.ToString().Trim() + file.FileName.Substring(file.FileName.LastIndexOf('.')).ToLower();
obj.IsDeleted = false;
obj.CreatedBy = long.Parse(Session["UserId"].ToString());
obj.CreatedOn = DateTime.Now;
obj.ModifiedBy = obj.CreatedBy;
obj.ModifiedOn = obj.CreatedOn;
Entities.ProImage_Shoping.Add(obj);
Entities.SaveChanges();

}
else
{

}


}
else
{

}
}