Problem filtering continuous form for empty or null string

[HS_1]

I am having problem filtering continuous form for empty ornull string. Wonder what I am doing wrong here?
This is what I have so far
Row Source:
SELECT DISTINCT tbl_Tracking.EHT_Zone
FROM tbl_Tracking
WHERElen(tbl_Tracking.EHT_Zone)>0
UNION Select "(Blank)"
FROM tbl_Tracking
ORDER BY tbl_Tracking.EHT_Zone;
When Debug.Print strEhtZoneI I see in immediate window


AND tbl_Tracking.EHT_Zone =((tbl_Tracking.EHT_Zone) Is NullOr (tbl_Tracking.EHT_Zone)="))

[CODEPrivate Sub cboEhtZone_AfterUpdate()
On Error GoTo Err_Handler
If Me.cboEhtZone.Value = "(Blank)" Then
strEhtZone = " AND tbl_Tracking.EHT_Zone =((tbl_Tracking.EHT_Zone) Is Null Or (tbl_Tracking.EHT_Zone)=""))"

Else
If Nz(Me.cboEhtZone, "") <> "" And Me.cboEhtZone <> "(Blank)" Then
strEhtZone = " AND tbl_Tracking.EHT_Zone = '" & Me.cboEhtZone & "'"
GetRecordSource
End If
End If
If GetListTotal = 0 Then
MsgBox "There are no records meeting the selected criteria ", vbExclamation, "No data"
cmdClearEhtZone_Click
End If
Debug.Print strEhtZone
Exit_Handler:
Exit Sub
Err_Handler:
MsgBox "Error " & Err.Number & " in Report_Open procedure : " & Err.Description
Resume Exit_Handler

End Sub][/CODE]

[June7]

The filter criteria is nonsense. Maybe you want

strEhtZone = " AND tbl_Tracking.EHT_Zone Is Null Or tbl_Tracking.EHT_Zone=''"

or simpler: " AND Nz(tbl_Tracking.EHT_Zone, '') = ''"

The string begins with AND so what other filter criteria is there?

Parentheses are critical when mixing AND and OR operators.

[HS_1]

Thanks June7 one mor time