Error checking for NULL in VBScript

Question

I have the following VBScript in a Classic ASP page:

function getMagicLink(fromWhere, provider)     dim url      url = "magic.asp?fromwhere=" & fromWhere     If Not provider is Nothing Then ' Error occurs here         url = url & "&provider=" & provider      End if     getMagicLink = "<a target='_blank' href='" & url & "'>" & number & "</a>" end function 

I keep getting an "Object Required" error messager on the line that says If Not provider Is Nothing Then.

Either the value is NULL, or it's not NULL, so why am I getting this error?

Edit: When I invoke the object, I pass in either NULL, or I pass in a string.

Answer 1

From your code, it looks like provider is a variant or some other variable, and not an object.

Is Nothing is for objects only, yet later you say it's a value that should either be NULL or NOT NULL, which would be handled by IsNull.

Try using:

If Not IsNull(provider) Then      url = url & "&provider=" & provider  End if 

Alternately, if that doesn't work, try:

If provider <> "" Then      url = url & "&provider=" & provider  End if 

Answer 2

I see lots of confusion in the comments. Null, IsNull() and vbNull are mainly used for database handling and normally not used in VBScript. If it is not explicitly stated in the documentation of the calling object/data, do not use it.

To test if a variable is uninitialized, use IsEmpty(). To test if a variable is uninitialized or contains "", test on "" or Empty. To test if a variable is an object, use IsObject and to see if this object has no reference test on Is Nothing.

In your case, you first want to test if the variable is an object, and then see if that variable is Nothing, because if it isn't an object, you get the "Object Required" error when you test on Nothing.

snippet to mix and match in your code:

If IsObject(provider) Then     If Not provider Is Nothing Then         ' Code to handle a NOT empty object / valid reference     Else         ' Code to handle an empty object / null reference     End If Else     If IsEmpty(provider) Then         ' Code to handle a not initialized variable or a variable explicitly set to empty     ElseIf provider = "" Then         ' Code to handle an empty variable (but initialized and set to "")     Else         ' Code to handle handle a filled variable     End If End If