Given the Actors table:

+-----------+------+
| Name      | Year |
+-----------+------+
| Nicolas   | 1980 | 
| Leonardo  | 1988 |
| Robert    | 1970 | 
| Adam      | NULL | 
+-----------+------+

How many records will the following query return?

SELECT * FROM Actors
WHERE Year IN (1970,1988,NULL);

Explanation

IS NULL or IS NOT NULL statements should be used to check for null / not null values.
All other types of comparisons (like =NULL, <>NULL, IN (NULL, ...)) are unreliable since they are evaluated to different results in different relational database management systems (False, UNKNOWN)