code: public void addColumn(String storeName, String rowKey, String columnName, String columnValue) {
          addColumn(storeName, rowKey, columnName, Utils.toBytes(columnValue));
      }
docs: Add or set a column with the given string value. The column value is converted to
  binary form using UTF-8.
  
  @param storeName Name of store that owns row.
  @param rowKey    Key of row that owns column.
  @param columnName   Name of column.
  @param columnValue  Column value as a string.