Is there a DBMS that allows the "= NULL" syntax?
Some implementations of SQL do recognise x = NULL as equality, the ISO/ANSI standard on the other hand does not. In SQL Server for instance, SET ANSI_NULLS OFF results in (NULL = NULL) = true.

SET ANSI_NULLS OFF
SELECT CASE WHEN NULL = NULL THEN 1 ELSE 0 END

SET ANSI_NULLS ON
SELECT CASE WHEN NULL = NULL THEN 1 ELSE 0 END