Is there any case when function available for this scenari?

Team,

CASE WHEN 'X' IS NULL THEN 'Y' ELSE 'X' END

Can be re-written as COALESCE('X','Y'). Is there any alternate function available for the following scenario: CASE WHEN 'X' IS NOT NULL THEN 'Y' ELSE 'X' END

Please help me with the same.

Thanks a lot!