case statement in where clause

I need a SQL statement that selects a specific year (@.yr type int) in the "createddate" column...if this @.yr is equal to 0 then I want to select ALL columns regardless of the year...

This is what I have so far, but it doesnt work...

SELECT * FROM tblUsers
WHERE year(CreatedDate)=CASE
WHEN @.yr<>'0' THEN @.yr
ELSE NOT NULL
END

SELECT * FROM tblUsers
WHERE year(CreatedDate)=CASE WHEN (@.yr= 0) THEN year(CreatedDate) ELSE @.yr END