query string is throwing exception for being null when its not - asp.net

Question

Here is whats happening , If the user is logged in - this is called directly from Page_Load
Protected Sub EnterNewTransInDb()
Dim conn As New SqlConnection(ConfigurationManager.ConnectionStrings("connstring").ConnectionString)
Dim comm As New SqlCommand("INSERT INTO tblRegisterRedirect (RegID , UserID, EventID, TimeStamp) VALUES (#RegID, #UserID, #EventID , getdate()) ;", conn)
Dim RegID As Guid
RegID = Guid.NewGuid()
Dim GIUDuserid As Guid
GIUDuserid = New Guid(HttpContext.Current.Request.Cookies("UserID").Value.ToString())
Dim GIUDevnetid As New Guid(HttpContext.Current.Request.QueryString("id").ToString())
comm.Parameters.AddWithValue("#RegID", RegID)
comm.Parameters.AddWithValue("#UserID", GIUDuserid)
comm.Parameters.AddWithValue("#EventID", GIUDevnetid)
Try
conn.Open()
Dim i As Integer = comm.ExecuteNonQuery()
conn.Close()
Catch ex As Exception
Dim errors As String = ex.ToString()
End Try
Dim URL As String = Request.QueryString("url").ToString()
Response.Redirect(URL + "?aid=854&rid=" + RegID.ToString())
End Sub
This works great, but if their not logged in , then they enter their log-in credentials - this happens on Button_Click event, in the click event I call this function EnterNewTransInDb() , When I run it this time , after logging in - SAME CODE , it throws an exception - Object reference is null - referring to the querystring
Protected Sub btnLogin_Click(sender As Object, e As System.EventArgs) Handles btnLogin.Click
'took out code SqlConnection onnection and SqlDataReader Code
dbCon.Open()
'If Email and PW are found
If dr.Read Then
Dim appCookie As New HttpCookie("UserID")
appCookie.Value = dr("GUID").ToString()
appCookie.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie)
Dim appCookie1 As New HttpCookie("UserName")
appCookie1.Value = dr("UserName").ToString
appCookie1.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie1)
Dim appCookie2 As New HttpCookie("UserEmail")
appCookie2.Value = txtEmail.Text.ToLower()
appCookie2.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie2)
Dim appCookie3 As New HttpCookie("Lat")
appCookie3.Value = dr("GeoLat").ToString()
appCookie3.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie3)
Dim appCookie4 As New HttpCookie("Long")
appCookie4.Value = dr("GeoLong").ToString()
appCookie4.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie4)
Dim appCookie5 As New HttpCookie("City")
appCookie5.Value = dr("City").ToString()
appCookie5.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie5)
Dim appCookie6 As New HttpCookie("State")
appCookie6.Value = dr("State").ToString
appCookie6.Expires = DateTime.Now.AddDays(30)
HttpContext.Current.Response.Cookies.Add(appCookie6)
HttpContext.Current.Response.Cookies("EO_Login").Expires = Now.AddDays(30)
HttpContext.Current.Response.Cookies("EO_Login")("EMail") = txtEmail.Text.ToLower()
Dim sUserData As String = HttpContext.Current.Server.HtmlEncode(HttpContext.Current.Request.Cookies("UserID").Value) & "|" & HttpContext.Current.Server.HtmlEncode(HttpContext.Current.Request.Cookies("UserName").Value) & "|" & HttpContext.Current.Server.HtmlEncode(HttpContext.Current.Request.Cookies("UserEmail").Value)
' Dim sUserData As String = "dbcf586f-82ac-4aef-8cd0-0809d20c70db|scott selby|scottselby#live.com"
Dim fat As FormsAuthenticationTicket = New FormsAuthenticationTicket(1, _
dr("UserName").ToString, DateTime.Now, _
DateTime.Now.AddDays(6), True, sUserData, _
FormsAuthentication.FormsCookiePath)
Dim encTicket As String = FormsAuthentication.Encrypt(fat)
HttpContext.Current.Response.Cookies.Add(New HttpCookie(FormsAuthentication.FormsCookieName, encTicket))
'If Email and Pw are not found
Else
dr.Close()
dbCon.Close()
End If
'Always do this
dr.Close()
sSql = "UPDATE eo_Users SET LastLogin=GETUTCDATE() WHERE GUID=#GUID; "
cmd = New SqlCommand(sSql, dbCon)
cmd.Parameters.AddWithValue("#GUID", HttpContext.Current.Session("UserID"))
cmd.ExecuteNonQuery()
dbCon.Close()
EnterNewTransInDb()
'Dim URL As String = Request.QueryString("url").ToString()
'Response.Redirect(URL + "?aid=854&rid=" + RegID.ToString())
End Sub

Answer 1

Assuming you only want this code to run if there is a valid QueryString, you could put a guard clause at the beginning of the method to simply check if QueryString is null and then perform some other action if this page is called without a QueryString.

Answer 2

Try setting the breakpoints before the call and make sure the variables are assigned values.

Answer 3

Have you tried putting a breakpoint on Dim URL As String = Request.QueryString("url").ToString() line in your code? Maybe you just need to evaluate first the querystring for the 'url' parameter, if it exists; before converting it to a string.