documentcloud/backbone — comment on commit 67f689df9c460c10c61d7a8722f303eb61d4b642
File: backbone.js line 488
By theasta:

It's not safe to compare to undefined since undefined is a variable that can be reassigned to any kind of value, including false in this case. It's probably better to compare to void 0 ( === void 0) or to null ( == null).