PL/SQL case statement

I am trying to hard code some values where the person_uid is null but I am geting the error message, "expecting from .." when I try to run it.  How  can this be fixed?

Set Pages 0 Lin 132 Trims On Feed Off Ver Off Head Off Emb On Term Off
Col File_Name Noprint New_Value File_Name

SELECT DISTINCT
         'FAC_'
      || UPPER (SUBSTR (academic_period_desc, 1, 2))
      || EXTRACT (YEAR FROM start_date)  || '.txt'
         AS file_name
FROM schedule_offering
WHERE academic_period = '200830';

Col Num_Cnt Noprint New_Value Num_Cnt
Spo &&File_Name
Prompt EXTERNAL_COURSE_KEY|EXTERNAL_PERSON_KEY|ROLE

SELECT REPLACE (   a.course_identification
                || a.offering_number
                || a.academic_period_desc,
                ' ',
                ''
      )
      || '|'
     CASE
         WHEN b.person_uid IS NULL
          THEN
             CASE
                WHEN A.DEPARTMENT = 'BIOL' THEN 112390
                WHEN A.DEPARTMENT = 'EDUC' THEN 112514
                WHEN A.DEPARTMENT = 'GNST' THEN 112534
                WHEN A.DEPARTMENT = 'MATH' THEN 112664
                WHEN A.DEPARTMENT = 'GEMS' THEN 112556
                WHEN A.DEPARTMENT = 'ART'  THEN 112365
                WHEN A.DEPARTMENT = 'LLC'  THEN 112600
                WHEN A.DEPARTMENT = 'MM'   THEN 112428
                WHEN A.DEPARTMENT = 'CHP'  THEN 112835
             END
           ELSE b.person_uid
         END
      || '|'
      || 'Instructor',
      ROWNUM num_cnt
FROM schedule_offering a, faculty b
WHERE     b.id(+) = a.primary_instructor_id
      AND b.academic_period(+) = '200830'
      AND b.faculty_member_status(+) = 'AC'
      AND a.academic_period = '200830'
      AND a.status = 'A'
      AND a.actual_enrollment > 0;
     -- AND a.active_offering_ind = 'Y';

SELECT   '***FileFooter'
      || '|'
      || trim('&&Num_Cnt')
      || '|'
      || TO_CHAR (SYSDATE, 'Hh24:Mi:Ss')
      || ' '
      || TO_CHAR (SYSDATE, 'Mm/Dd/Yyyy')
FROM DUAL;

Spo Off