Validate world in CraftServer.createChunkData

src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -1684,6 +1684,7 @@ public final class CraftServer implements Server {
 
     @Override
     public ChunkGenerator.ChunkData createChunkData(World world) {
+        Validate.notNull(world, "World cannot be null");
         return new CraftChunkData(world);
     }