Bukkit/CraftBukkit — comment on commit 0cffd7f7b04f0e045d4184cfc259a81004b97b51
File: src/main/java/org/bukkit/craftbukkit/CraftArt.java line 36
By feildmaster:

It needs return null, because of java. :P

It expects a "return" value. The null is there to make it happy.