Problem with Web Service ASMX when consuming it from Android

I have a problem with the web service in asmx that saves images and that I consume from an Android app:

This is the error it generates:

  

System.NullReferenceException: Object reference not set as   instance of an object. in   WebServicesLogistica.ServicesLogistica.CreateRequest () in   c: \ Users \ SUPPORT \ Desktop \ PROJECT   LOGISTICS \ WebSistemaLogisticoR \ WebServicesLogistica \ WebServi cesLogistica \ Service sLogistica.asmx.cs: l line   303

Service code:

  [WebMethod]    
    public void SaveImage()
    {
        try
        {
            if (!System.IO.Directory.Exists(HttpContext.Current.Server.MapPath("~/Upload")))
            {
                System.IO.Directory.CreateDirectory(HttpContext.Current.Server.MapPath("~/Upload/"));
            }

            string path = HttpContext.Current.Server.MapPath("~/Upload/").ToString();
            var Request = HttpContext.Current.Request;
            if (Request.Files.Count > 0)
            {
                var file = Request.Files[0];
                file.SaveAs(path + file.FileName);
            }  
        }

    catch(Exception ex){
        throw ex;
    }
  }

Command in multipart/form-data