code: public void addColumn(String storeName, String rowKey, String columnName) {
          addColumn(storeName, rowKey, columnName, EMPTY);
      }
docs: Add a column with empty value. The value will be empty byte array/empty string, not null
  
  @param storeName Name of store that owns row.
  @param rowKey    Key of row that owns column.
  @param columnName   Name of column.