Why does case statement in Oracle doesn't work for string comparisons?

Question

I'm puzzled by this in Oracle

select case when 'hello' <> '' then 1 else 2 end from dual;

returns 2

select case when 'hello' <> 'hello' then 1 else 2 end from dual;

returns 2

however on SQL*Server this works as expected.

Answer 1

Empty string in Oracle acts as null - so your comparison <> null will be always false...
(edit proposed by igr)