thoughtbot/bourbon — pull request #398 by bretmorris (2014-04-15 22:48:16+00:00)
Title: Update position doc to use `null`.

As of Bourbon v4.0+ `null` must be specified instead of unit-less values if the user intends to ignore certain position values. See https://github.com/thoughtbot/bourbon/issues/397#issuecomment-40538791.