vbscript ADO Recordset Update - vbscript

Question

I am trying to update paths in access mdb database using ADO and vb6 without success.
The scripts are below. The line Rs1(columnName) = Replace( Rs1(columnName),oldPath,newPath) causes vbscript runtime err invalid use of Null.
Put simply, I want to update all tables that have strings like \\server2 to \\DBSE-46\. I
am running the script on win7 64bit as
c:\windows\syswow64\cscript.exe C:\SQLTest\HarishScripts\DatabaseAccessProg6.vbs >> C:\SQLTest\HarishScripts\DatabaseAccessProg6.txt
Option Explicit
WScript.Echo "START of ADO access program...."
Dim DBpath
Dim tableName
Dim columnName
Dim oldPath
Dim newPath
'#######################################################################################
' Set all external variables here...
DBpath = "C:\DBTest;"
tableName = "Test"
columnName = "Path"
oldPath = "\\SERVER2\"
newPath = "\\DBSE-46\"
'#######################################################################################
Dim Rs1
Set Rs1 = CreateObject("ADODB.Recordset")
Dim i
Dim AccessConnect
AccessConnect = "Driver={Microsoft Access Driver (*.mdb)};" & _
"Dbq=MedDataSource.mdb;" & _
"DefaultDir=" & DBpath & _
"Uid=Admin;Pwd=;"
'--------------------------
' Recordset Object Method
'--------------------------
' Recordset Open Method #4: Open w/o Connection & w/Connect String
Dim sqlStmt
sqlStmt = "SELECT * FROM " & tableName
' use LockTypeEnum.adLockOptimistic = 3. This allows update of the recordset.
Rs1.LockType = 3
Rs1.Open sqlStmt, AccessConnect
Do Until Rs1.EOF
'WScript.Echo Rs1("Path")
if (Rs1(columnName) = NULL) Then
End If
Rs1(columnName) = Replace( Rs1(columnName),oldPath,newPath)
Rs1.MoveNext
Loop
' Close the recordset...
Rs1.Close
Set Rs1 = Nothing
WScript.Echo "..."
WScript.Echo "..."
WScript.Echo "DONE!"

Answer 1

Use the IsNull function to check for Null values. In my older local .chm there is even a paragraph
Use the IsNull function to determine whether an expression contains a
Null value. Expressions that you might expect to evaluate to True
under some circumstances, such as If Var = Null and If Var <> Null,
are always False. This is because any expression containing a Null is
itself Null, and therefore, False.
Work on your understanding of the If clause. In
if (Rs1(columnName) = NULL) Then
End If
Rs1(columnName) = Replace( Rs1(columnName),oldPath,newPath)
the last statement will be executed regardless of the content of Rs1(columnName). So do
if Not IsNull(Rs1(columnName)) Then
Rs1(columnName) = Replace( Rs1(columnName),oldPath,newPath)
End If