Please help me fix this IF statement

I can't get this code to go through. What am I missing?

This is a new statement which is part of an internal database but I cannot get it to accept the code.

SELECT "Human Resources - Assignment EIT Details"."Employment Attributes"."Employee Latest Start Date", "Assignment"."Incremental Date"

CASE

WHEN "Assignment"."Incremental Date" IS NULL THEN "Human Resources - Assignment EIT Details"."Employment Attributes"."Employee Latest Start Date"
ELSE "Assignment"."Incremental Date" END;

I expect the output to show the Incremental Date but if the field IS NULL then it needs to show the Employee Latest Start Date