openlayers/ol3 — pull request #161 by elemoine (2013-01-28 11:48:17+00:00)
Title: Do not draw image if image is null

With this PR the Canvas 2D map renderer does not draw a `null` image returned by a layer renderer.

I need this case to be handled in my single image work. Tom is going to work on optimizing the Canvas 2D renderer. This PR aims to avoid conflicts between his work and mine.