SQL & PL/SQL :: Rows With Column Value Always NULL

I have a table with columns emp_i, LOC_C and SUBSID_C. I want to find all emp_i's with LOC_C OR SUBSID_C as always NULL. Please note that the value should be NULL, always, for all dates.

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EX:
emp_i----LOC_C---SUBSID_C--Eff_Date
100------20------30--------01/01/2011
101------NULL----10--------05/01/2011
102------NULL----NULL------02/01/2011
101------20------NULL------02/01/2011
102------NULL----NULL------05/01/2011
103------NULL----20--------01/01/2011
103------NULL----NULL------02/01/2011
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The query ---
should return 102 as LOC_C OR SUBSID_C is ALWAYS NULL.
should return 103 as LOC_C is ALWAYS NULL.
should not return 101, as LOC_C is not ALWAYS NULL.
In other words, the query should give list of emp_i who never ever had a non-null value for LOC_C OR SUBSID_C. The purpose is to find the emp_i for which the columns LOC_C and SUBSID_C are never used.

I tried the query:
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SELECT DISTINCT ORG_EMP_I FROM tab1
WHERE ORG_GRP_I = 58
AND ORG_EMP_I NOT IN (
SELECT DISTINCT org_emp_i
FROM tab1 ap
WHERE ap.ORG_GRP_I = 58
AND trim(ap.LOC_C) IS NOT NULL OR ap.ORG_SBSID_C IS NOT NULL )
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