code: private void writeSymbolMap(ByteBuf out) {
          Bzip2BitWriter writer = this.writer;
  
          final boolean[] blockValuesPresent = this.blockValuesPresent;
          final boolean[] condensedInUse = new boolean[16];
  
          for (int i = 0; i < condensedInUse.length; i++) {
              for (int j = 0, k = i << 4; j < HUFFMAN_SYMBOL_RANGE_SIZE; j++, k++) {
                  if (blockValuesPresent[k]) {
                      condensedInUse[i] = true;
                  }
              }
          }
  
          for (boolean isCondensedInUse : condensedInUse) {
              writer.writeBoolean(out, isCondensedInUse);
          }
  
          for (int i = 0; i < condensedInUse.length; i++) {
              if (condensedInUse[i]) {
                  for (int j = 0, k = i << 4; j < HUFFMAN_SYMBOL_RANGE_SIZE; j++, k++) {
                      writer.writeBoolean(out, blockValuesPresent[k]);
                  }
              }
          }
      }
docs: Write the Huffman symbol to output byte map.