facebook/facebook-ios-sdk — pull request #566 by epatey (2013-12-20 18:23:14+00:00)
Title: Fix FBImageResourceLoader to return the non-retina image rather than nil when retina is preferred but not available.

The 'blank' images used by FBProfilePictureView, for example, have no retina versions.
i.e. FBProfilePictureViewBlankProfileSquarePNG