Bukkit/CraftBukkit — pull request #1132 by lenis0012 (2013-04-07 15:05:18+00:00)
Title: Fixed NPE on constructing of invalid signs. Fixes BUKKIT-3936

When a sign is contructed and the TileEntity does not exist the lnes
throw an NPE.

This can be fixed by adding null checks before the lines need to do
their job