nomad/houston — pull request #32 by jerryhjones (2013-12-13 18:48:36+00:00)
Title: The sound key must be present and nil to send silent/hidden push notifications

If the sound key is not present, truly silent push notifications are never delivered. That is, notifications without a sound or a message, but probably with the content-available bit flipped. Strange as it may be, a nil value assigned to the sound key fixes this issue.