mozilla/addon-sdk — pull request #1206 by Gozala (2013-08-19 20:47:32+00:00)
Title: Bug 905516 - This mitigates problem by making intention explicit.

Erik this is solution very similar to yours, it just makes it explicit that code intentionally passes undefined. Also while it's not a constraint to SDK, method lib performance is very much constraint for other users and this saves one lookup.