Please help i wanted to use the update panel to stop the page from posting changes before i complete the transaction but it is flagging the error below please help.

System.NullReferenceException: 'Object reference not set to an instance of an object.'
System.Web.UI.WebControls.FileUpload.PostedFile.get returned Nothing.

    Protected Sub Upload(sender As Object, e As EventArgs) Handles btnUpload.Click
        Dim filename As String = Path.GetFileName(FileUpload1.PostedFile.FileName)
        If filename = "" Then
            updatedata2000()
        Else
            updatedata()
            Dim contentType As String = FileUpload1.PostedFile.ContentType
            Using fs As Stream = FileUpload1.PostedFile.InputStream
                Using br As New BinaryReader(fs)
                    Dim bytes As Byte() = br.ReadBytes(DirectCast(fs.Length, Long))
                    Dim constr As String = ConfigurationManager.ConnectionStrings("INTERVIEWSConnectionString").ConnectionString
                    Using con As New SqlConnection(constr)
                        Dim query As String = "insert into tblFiles values (@Name, @ContentType, @Data,@admno,@Studentnames,@comments)"
                        Using cmd As New SqlCommand(query)
                            cmd.Connection = con
                            cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename
                            cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contentType
                            cmd.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes
                            cmd.Parameters.Add("@admno", SqlDbType.Binary).Value = admno.Text
                            cmd.Parameters.Add("@Studentnames", SqlDbType.Binary).Value = StudentNames.Text
                            cmd.Parameters.Add("@comments", SqlDbType.Binary).Value = commentsdatakt.Text
                            con.Open()
                            cmd.ExecuteNonQuery()
                            con.Close()
                        End Using
                    End Using
                End Using
            End Using

            Response.Redirect(Request.Url.AbsoluteUri)
        End If