docs: protected int[] colsBitsetToIDs(BitSet cols) {
      int[] colIDs = new int[cols.cardinality()];
      int colsIndex = 0;
      for(int i = cols.nextSetBit(0); i >= 0; i = cols.nextSetBit(i + 1)) {
        colIDs[colsIndex] = i;
        colsIndex++;
      }
      return colIDs;
    }