object reference not set to an instance of an object.

Question

When i run below code it gives "object reference not set to an instance of an object."Exception on first line.

if ((context.Session["ImageBytes"]) != null)

        {

            byte[] image = (byte[])(context.Session["ImageBytes"]);

            context.Response.ContentType = "image/JPEG";

            context.Response.BinaryWrite(image);

        }