WRITE / '***********BKPF**********'.

DATA: LS_BKPF TYPE BKPF.

  SELECT fieldname position
    INTO CORRESPONDING FIELDS OF TABLE lt_key
    FROM dd03l
    WHERE tabname = 'BKPF'
      AND as4local = 'A'
      ORDER BY position.

DELETE lt_key WHERE fieldname CP '.*'.

LOOP AT lt_key INTO ls_key.
  CLEAR: LS_CONDITION.

*  CONCATENATE ls_key-fieldname 'IS NOT NULL'
  CONCATENATE ls_key-fieldname '<> SPACE'
    INTO LS_CONDITION SEPARATED BY SPACE.

  SELECT SINGLE *
    FROM BKPF
    INTO LS_BKPF
    WHERE (LS_CONDITION).

  IF SY-SUBRC <> 0.
    WRITE / ls_key-fieldname.
  ENDIF.

ENDLOOP.