docs: @Override
    public void serialize(DataOutput out) throws IOException {
      // TODO: Should we transport the performance tweak 'doCacheCardinalities'?
      out.writeBoolean(signedLongs);
  
      out.writeInt(highToBitmap.size());
  
      for (Entry<Integer, BitmapDataProvider> entry : highToBitmap.entrySet()) {
        out.writeInt(entry.getKey().intValue());
        entry.getValue().serialize(out);
      }
    }