[BUG] NULL = NULL in the join expression is different from the value of mysql

[xinyiZzz]

Describe the bug

1. query 1:

SELECT * FROM tab1 INNER JOIN tab0 ON NULL = NULL

NULL = NULL in Mysql is false
NULL = NULL in Doris is true

2. In contrast, query 2:

SELECT * FROM tab1 where NULL = NULL

NULL = NULL is false in both Doris and Mysql

In addition, the conclusion is the same in NULL NOT BETWEEN NULL AND (NULL ), NULL <> NULL, NULL <= NULL.

Found through the sqllogictest test case.