select case when dummy is null then ‘*null*’ else ‘in else’ end
from dual;

For completeness :

case var when val_1 then ‘x’ else ‘y’ end

is the same as

case when var = val_1 then ‘x’ else ‘y’ end

whereas

case var when null then ‘x’ else ‘y’ end

is the same as

case when var = null then ‘x’ else ‘y’ end

which is different to what you want

case when var is null then ‘x’ else ‘y’ end

I think you may have a point. However when you try the syntax you suggested :
SQL> l
1 SELECT team, best,
2 CASE winners WHEN winners IS NULL THEN
3 CASE runner_up WHEN runner_up IS NULL THEN
4 CASE third WHEN third IS NULL THEN fourth ELSE third END
5 ELSE runner_up END
6 ELSE winners END years
7* FROM final_four
SQL> /
CASE winners WHEN winners IS NULL THEN
*
ERROR at line 2:
ORA-00905: missing keyword

This is the same when you reverse the logic ( i.e. WHEN winners IS NOT NULL).
This example is in SQL on Oracle 10g XE ( I also tried the stuff in the original post on 11gR2).

Not sure if you’re example works on another RDBMS, but unfortunately, Oracle’s having none of it.

Glen