Asp.net - Object reference not set to an instance of an object - asp.net

Question

I am using the following to control user log in authentication. This redirects fine when the user is inactive or locked out, but when the user is deleted from the database, I get an error message...
"Object reference not set to an instance of an object" on this line...
If currentuser IsNot Nothing And currentuser.IsApproved = False Or currentuser.IsLockedOut = True Then
What could be causing this to happen?
Protected Sub Page_Init(sender As Object, e As System.EventArgs) Handles Me.Init
If User.Identity.IsAuthenticated Then
Dim currentuser As MembershipUser = Membership.GetUser()
If currentuser IsNot Nothing And currentuser.IsApproved = False Or currentuser.IsLockedOut = True Then
FormsAuthentication.SignOut()
FormsAuthentication.RedirectToLoginPage()
End If
If currentuser IsNot Nothing Then
Response.Redirect("~/media")
End If
End If
End Sub

Answer 1

Change the If condition to:
If currentuser IsNot Nothing Then
If currentuser.IsApproved = False Or currentuser.IsLockedOut = True Then
FormsAuthentication.SignOut()
FormsAuthentication.RedirectToLoginPage()
End If
Response.Redirect("~/media")
End If

Answer 2

You need to parathesize the second part and use OrElse/AndAlso, otherwise currentuser IsNot Nothing will not be applied to all parts of your if
So this will fix it:
If currentuser IsNot Nothing AndAlso (Not currentuser.IsApproved OrElse currentuser.IsLockedOut) Then
Don't use Or (and AND) but OrElse (and AndAlso) which will short circuit. That means it will not evaluate the second part if the first part was already true. Or (and And) on the other side will evaluate both parts always.

Answer 3

Since 'And' receives precedence over 'Or' the expression will
be evaluated as follows:
If
{
currentuser IsNot Nothing And currentuser.IsApproved = False //condition 1
Or
currentuser.IsLockedOut = True //condition 2
}
Then..
If current user is in fact nothing:
condition 1- will not fail, but condition 2 will throw
an exception since the code is trying to evaluate (nothing).somthing.
To fix the problem you'll have to add parentheses as shown:
If
currentuser IsNot Nothing //condition 1
And
(currentuser.IsApproved = False Or currentuser.IsLockedOut = True) //condition 2
Then..
Now, the 2nd condition will be evaluated only if the first condition is true.