Minecraft 15w49a, Minecraft 15w49b, Minecraft 15w50a, Minecraft 15w51a, Minecraft 15w51b, Minecraft 16w02a, Minecraft 16w03a
If there are empty (completely air) chunks in view, when the game attempts to create an icon for the world, the icon will be black (transparent?).
Steps to reproduce:
1. Create a new world (easiest with Void Superflat)
2. Look at an area with missing or empty chunks
3. Press esc to trigger the icon generation
4. Save and quit, then look at the new icon generated.