Bug #9938 VIEW, OUTER JOIN, EXPLICIT COALESCE, wrong result

Description:
A have a test case derived from the NIST tests where I got correct results 
till yesterday (2005-April-14). Since today I get wrong results.

CREATE TABLE t1 (EMPNUM INT, GRP INT);
INSERT INTO t1 VALUES (0, 10);
INSERT INTO t1 VALUES (2, 30);

CREATE TABLE t2 (EMPNUM INT, NAME CHAR(5));
INSERT INTO t2 VALUES (0, 'KERI');
INSERT INTO t2 VALUES (9, 'BARRY');

CREATE VIEW v1 AS
SELECT COALESCE(t2.EMPNUM,t1.EMPNUM) AS EMPNUM,
NAME, GRP FROM t2 LEFT OUTER JOIN t1 USING (EMPNUM);
# Note: COALESCE was used to bypass other open bugs.

SELECT * FROM v1 WHERE EMPNUM = 9 ;
EMPNUM  NAME    GRP
                          <--- This empty result is wrong.
SELECT * FROM v1 WHERE NAME = 'BARRY';
EMPNUM  NAME    GRP
9       BARRY   NULL

It looks like the bug appears if 
- a column value is coalesced with a "special" NULL column 
  value. "special" NULL means, that this NULL is result of the 
  outer join row completion.
- there is a qualification for this coalesced column (EMPNUM)
- a view seems to be needed

My environment:
   - Intel PC with Linux(SuSE 9.1)
   - MySQL compiled from source
        Version 5.0 ChangeSet@1.1836, 2005-04-14

How to repeat:
Please use the attached test case ml96.test , 
copy it to mysql-test/t

  touch r/ml96.result     # Produce a dummy file with expected
                                  # results.
  ./mysql-test-run ml96
  inspect r/ml96.reject    # The protocol of the execution.

test case with variations of the problem + comments

Attachment: ml96.test (application/test, text), 3.82 KiB.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/internals/25159

The not_null_tables method for class Item_ref was missing.

ChangeSet
  1.1897 05/05/21 08:44:50 igor@rurik.mysql.com +3 -0
  join_outer.test, join_outer.result:
    Added test cases for bug #9938.
  item.h:
    Fixed bug #9938: missing method not_null_tables for Item_ref.

Fix will appear in  release 5.0.7.

Noted in 5.0.7 changelog.