code: @SubscribeEvent
  	public void onDataSave(ChunkDataEvent.Save event)
  	{
  		Set<BlockPos> coords = chunks(event.getChunk()).get(event.getChunk());
  		if (!coords.isEmpty())
  			writeLongArray(event.getData(), coords);
  	}
docs: Called when a {@link Chunk} is saved on the server.<br>
  Writes the coordinates to be saved in the Chunk's NBT.
  
  @param event the event