woothemes/woocommerce — pull request #6641 by coenjacobs (2014-10-28 12:15:19+00:00)
Title: Allow to filter empty tax rate code

As discussed with @mikejolley earlier today: When using an external tax rate storage, the `get_rate_code` method will return an empty string because there are no rates stored in the database. This change allows to filter the empty value before returning it, so it can be modified to use codes from the external tax rate storage.