incorrect result - case when (not null is null) then true else false end

postgres=# select (case when (not null is null) then true else false end) from (values(1)) foo;
 case
------
 f
(1 row)

0: jdbc:calcite:model=target/test-classes/mod> select (case when (not null is null) then true else false end) from (values(1));
+--------+
| EXPR$0 |
+--------+
| false  |
+--------+
1 row selected (1.271 seconds)

0: jdbc:drill:schema=dfs.tmp> select (case when (not null is null) then true else false end) from (values(1));
+---------+
| EXPR$0  |
+---------+
| true    |
+---------+
1 row selected (0.096 seconds)