again, simple case statement

 I have this very simple case statemnt.  I've trying to ensure that all values are PNC for the campus column but I still values other than PNC.  I've checked and there are no null values in the campus column. Why isn't the case statement working?

SELECT person_uid,
            ID,
            campus,
            CASE
               WHEN campus IS NOT NULL
                   THEN  
                                 'PNC'
                   ELSE
                               'CAMPUS'
            END
               REPORTING_CAMPUS
       FROM frz_academic_study