Shopify/active_merchant — pull request #1360 by brianphillips (2014-08-28 15:58:41+00:00)
Title: allow for clearing expiration date on a profile

According to the Orbital docs:

To clear any legacy data, the XML tag is submitted with nothing but a tilde (~), as in the
example below:
~

This is useful in the case of trying to rebill a subscription and the first attempt fails due to an expired card (i.e. `33`)