Autofilter with multiple criteria - how to ignore blank criteria

Hi,

I have the following code:

Sub searchfilter()
'
' Search page filter
'
'
    ActiveSheet.Range("$A$4:$K$6000").AutoFilter field:=3, Criteria1:=ActiveSheet.Range("c2")
    ActiveSheet.Range("$A$4:$K$6000").AutoFilter field:=6, Criteria1:=ActiveSheet.Range("D2")
    ActiveSheet.Range("$A$4:$K$6000").AutoFilter field:=8, Criteria1:=ActiveSheet.Range("E2")

End Sub

However it requires all cell ranges , C2, D2, and E2 to have a value to filter or it displays blank lines only. How do you adjust the above code to allow it to ignore a cell if there is no search criteria entered into it?

Thanks