ItemStaff.java

MinecraftServer server = player.getEntityWorld().getMinecraftServer();
        WorldServer worldServer = server.getWorld(dimension);
        player.addExperienceLevel(0);

        if (worldServer == null || worldServer.getMinecraftServer() == null){ //Dimension doesn't exist
            throw new IllegalArgumentException("Dimension: "+dimension+" doesn't exist!");
        }

        worldServer.getMinecraftServer().getPlayerList().transferPlayerToDimension(entityPlayerMP, dimension, new DimTeleporter(worldServer, x, y, z));
        player.setPositionAndUpdate(x, y, z);
        if (oldDimension == 1) {
            // For some reason teleporting out of the end does weird things. Compensate for that
            player.setPositionAndUpdate(x, y, z);
            worldServer.spawnEntity(player);
            worldServer.updateEntityWithOptionalForce(player, false);
        }