VBA Date Filtering Issue

[telobamipada]

I am using the below vba code to filter a spreadsheet on open to show the current month and all future dates and I can't for the life of me get it to show null values... where the date isn't populated. Any help would be appreciated!

Private Sub Workbook_Open()
Sheets("Sheet1").Select
'startdate as date
Dim startDate As Date
'startdate as long for excel
Dim lstartDate As Long
'get start date, day = always 1
startDate = DateSerial(Year(Now), Month(Now), 1)
lstartDate = startDate
'filter everything before current month
'you see this month + future
ActiveSheet.Range("A1").AutoFilter Field:=6, Criteria1:=">=" & lstartDate
End Sub