Both the $.fn.scrollTop and $.fn.scrollLeft setters return null when called on an empty jquery object. This leads to unexpected null pointer exceptions. Example:

#!js
// Causes null pointer exception
$(".does-not-exists").scrollTop(100).addClass("scrolled");

This is also inconsistant behavior. Most jquery setters (e.g. height, width, addClass, attr, css, etc...) always return jquery objects.