get_course_by_id is used all over the place, in cms and common as well as lms.  So I'm going to keep this as-is.  I agree that a simpler method would be useful where we don't need a response.  Say "get_course_instance".  But I'm just going to have it return a ValueError instead of a KeyError or ItemNotFoundError or InvalidLocationError, because generally the distinction is not important to the caller.