help field value not being inserted

I created the following trigger to insert a record into table b when a record in table a is updated. see trigger below:

______________________________________________
CREATE or REPLACE TRIGGER rwt_BIB_HOLDINGS_U
AFTER UPDATE ON BIB_HOLDINGS
FOR EACH ROW
DECLARE
  mp_count    NUMBER;
  sp_count    NUMBER;
BEGIN
        SELECT COUNT (*) INTO mp_count FROM rwu_bib_holdings where site=:new.site and pdf_name=:new.pdf_name;

        SELECT COUNT (*) INTO sp_count FROM rwu_bib_holdings_single where site=:new.site and pdf_name=:new.pdf_name;



  IF mp_count = 0 THEN
                INSERT INTO RWU_BIB_HOLDINGS (seq_num, site, pdf_name, action, bh_id) VALUES (RWU_BIB_HOLDINGS_SEQ.nextval, :new.site, :new.pdf_name, 'U', :new.id);

        END IF;
  IF mp_count = 0 THEN
                INSERT INTO RWU_BIB_HOLDINGS_SINGLE (seq_num, site, pdf_name, action, bh_id) VALUES (RWU_BIB_HOLDINGS_SEQ.nextval, :new.site, :new.pdf_name, 'U', :new.id);

        END IF;
END;
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however, the field bh_id is not being populated. Could someone tell me what is wrong with my trigger that is preventing this field population?

SQL> update bib_holdings set site='SENSIAC' where site='CBIAC' and rownum<2;

1 row updated.

SQL> commit;

Commit complete.

SQL> select * from rwu_bib_holdings;

   SEQ_NUM SITE       PDF_NAME   A      BH_ID
---------- ---------- ---------- - ----------
   1803210 SENSIAC    CB-122392  U
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