Bug #42114 aggregation function with a null criterion and indexing returns wrong data

Description:
preforming an aggregate function over data, with a where condition evaluating to NULL and index on the relevant column returns wrong and inconsistent data.

How to repeat:
--------------
DROP TABLE IF EXISTS a
--------------

--------------
CREATE TABLE a (b int not null)
--------------

--------------
INSERT INTO a (b) values (1),(2),(3),(4)
--------------

--------------
SELECT MAX(b) FROM a where b > 2
--------------

+--------+
| MAX(b) |
+--------+
|      4 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < 2
--------------

+--------+
| MAX(b) |
+--------+
|      1 | 
+--------+
--------------
SELECT MAX(b) FROM a where b > NULL
--------------

+--------+
| MAX(b) |
+--------+
|   NULL | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|   NULL | 
+--------+
--------------
ALTER TABLE a ADD INDEX (b)
--------------

--------------
SHOW CREATE TABLE a
--------------

*************************** 1. row ***************************
       Table: a
Create Table: CREATE TABLE `a` (
  `b` int(11) NOT NULL,
  KEY `b` (`b`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
--------------
SELECT MAX(b) FROM a where b > 2
--------------

+--------+
| MAX(b) |
+--------+
|      4 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < 2
--------------

+--------+
| MAX(b) |
+--------+
|      1 | 
+--------+
--------------
SELECT MAX(b) FROM a where b > NULL
--------------

+--------+
| MAX(b) |
+--------+
|   NULL | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|      3 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|      2 | 
+--------+
--------------
SELECT MAX(b) FROM a where b > NULL
--------------

+--------+
| MAX(b) |
+--------+
|   NULL | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|      3 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|      2 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|      1 | 
+--------+
--------------
SELECT MAX(b) FROM a where b < NULL
--------------

+--------+
| MAX(b) |
+--------+
|   NULL | 
+--------+
--------------
SELECT VERSION()
--------------

+-----------+
| VERSION() |
+-----------+
| 5.1.30    | 
+-----------+

Verified just as described with 5.1.30 on Windows:

C:\...Files\MySQL\MySQL Server 5.1\bin>mysql -uroot -proot -P3307 test
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.1.30-enterprise-gpl-advanced MySQL Enterprise Server - Advance
d Edition (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> drop table a;
Query OK, 0 rows affected (0.02 sec)

mysql> CREATE TABLE a (b int not null) engine=MyISAM;
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO a (b) values (1),(2),(3),(4);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT MAX(b) FROM a where b > 2;
+--------+
| MAX(b) |
+--------+
|      4 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b <2;
+--------+
| MAX(b) |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b < NULL;
+--------+
| MAX(b) |
+--------+
|   NULL |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b > NULL;
+--------+
| MAX(b) |
+--------+
|   NULL |
+--------+
1 row in set (0.00 sec)

mysql> ALTER TABLE a ADD INDEX (b);
Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT MAX(b) FROM a where b > 2;
+--------+
| MAX(b) |
+--------+
|      4 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b <2;
+--------+
| MAX(b) |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b > NULL
    -> ;
+--------+
| MAX(b) |
+--------+
|   NULL |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b <NULL;
+--------+
| MAX(b) |
+--------+
|      3 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b > NULL;
+--------+
| MAX(b) |
+--------+
|   NULL |
+--------+
1 row in set (0.00 sec)

mysql> SELECT MAX(b) FROM a where b < NULL;
+--------+
| MAX(b) |
+--------+
|      2 |
+--------+
1 row in set (0.00 sec)

mysql> explain select MAX(b) FROM a where b < NULL\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: NULL
         type: NULL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: NULL
        Extra: Select tables optimized away
1 row in set (0.00 sec)

Duplicate of BUG#47762.