code: public static RowColumn toRowColumn(Key key) {
      if (key == null) {
        return RowColumn.EMPTY;
      }
      if ((key.getRow() == null) || key.getRow().getLength() == 0) {
        return RowColumn.EMPTY;
      }
      Bytes row = ByteUtil.toBytes(key.getRow());
      if ((key.getColumnFamily() == null) || key.getColumnFamily().getLength() == 0) {
        return new RowColumn(row);
      }
      Bytes cf = ByteUtil.toBytes(key.getColumnFamily());
      if ((key.getColumnQualifier() == null) || key.getColumnQualifier().getLength() == 0) {
        return new RowColumn(row, new Column(cf));
      }
      Bytes cq = ByteUtil.toBytes(key.getColumnQualifier());
      if ((key.getColumnVisibility() == null) || key.getColumnVisibility().getLength() == 0) {
        return new RowColumn(row, new Column(cf, cq));
      }
      Bytes cv = ByteUtil.toBytes(key.getColumnVisibility());
      return new RowColumn(row, new Column(cf, cq, cv));
    }
docs: Converts from an Accumulo Key to a Fluo RowColumn
  
  @param key Key
  @return RowColumn