SELECT w.* FROM work_log1 AS w, [task name] AS t WHERE t.task_name=forms!
[Accenture QC]!combo4 And t.task_id=w.task_name And w.activity_start_date Between
forms ![Accenture QC]!text0 And forms![Accenture QC]!text11
and w.[TAT] = forms![Accenture QC]!combo46

and iif(forms![Accenture QC]!combo46 = '', t.task_id=w.task_name ,
t.task_id=w.task_name   and w.[TAT] = forms![Accenture QC]!combo46)

"SELECT w.* FROM work_log1 AS w where (w.[TAT] = forms![Accenture QC]!combo46
OR forms![Accenture QC]!combo46 Is Null)"

and w.[TAT] = forms![Accenture QC]!combo46

AND (w.[TAT] = forms![Accenture QC]!combo46
    OR forms![Accenture QC]!combo46 Is Null)

Len(Trim(forms![Accenture QC]!combo46 & "")) = 0

SELECT w.*
FROM work_log1 AS w
where
       w.[TAT] = forms![Accenture QC]!combo46
    OR Len(Trim(forms![Accenture QC]!combo46 & "")) = 0