docs: public byte[] columnQualifier() {
      if (display_name == null || display_name.isEmpty()) {
        throw new IllegalArgumentException("Missing display name");
      }
      
      final byte[] qualifier = new byte[LEAF_PREFIX.length + 4];
      System.arraycopy(LEAF_PREFIX, 0, qualifier, 0, LEAF_PREFIX.length);
      System.arraycopy(Bytes.fromInt(hashCode()), 0, qualifier, 
          LEAF_PREFIX.length, 4);
      return qualifier;
    }