SQL retrieving records where a field isNull

In Excel I am retrieving data in vba using sql.

I have the following code;


Function SummarySQL()

Dim FirstDate As Date
Dim Sector As String
Dim Team As String
Dim TabCode As String

FirstDate = Range("FirstDate").Value
Sector = Range("Sector").Value
Team = Range("Team").Value
TabCode = "Additional Resources"

If Sector = "Show All" Then
    Sector = "%"
End If

If Team = "Show All" Then
    Team = "%"
End If

SummarySQL = "SELECT * FROM [" & DataRange & "] WHERE [Month Year] = " & CDbl(FirstDate) & " " & _
             "AND [Sector] Like '" & Sector & "'" & " " & _
             "AND [TabCode] Like '" & TabCode & "'" & " " & _
             "AND [Team] Like '" & Team & "'" & ";"

End Function


Sometimes the Sector field will have been left empty, so where it's returning all with %, I also need it to return the nulls too.  When Sector <> % I don't want the nulls.

i hope this makes sense.

Thanks in advance.