How to make a file upload control optional?

Greetings,
I've created a message board with a file upload control, this should be optional. So for example if people don't want to upload a picture with their message it should not return in an error.

c# code:
//Getting dbconnection from web.config connectionstring SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["dbgreatforestConnectionString"].ToString()); //Open the database connection con.Open(); //Get Filename from fileupload control string filename = Path.GetFileName(fileuploadimages.FileName); //Save images into Images folder fileuploadimages.SaveAs(Server.MapPath("Uploads/" + filename));   //Query to insert images path and name into database SqlCommand cmd = new SqlCommand("Insert into msgs(msg, titel, naam, date, msgpic) values(@msg, @titel, @naam, @date, @msgpic)", con); //Passing paramet ...