Allowing Null when uploading Images

I have this codebehind page to upload multiple images into filesystem, and the path into the SQL database. Is there a way to modify the code so if the user doesn't upload an image for a certain field, it doesn't give an error.
 
using System;
using System.IO;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Web.Services.Protocols;

public partial class _Default : System.Web.UI.Page
{

protected void In ...