docs: public ZipFileData addFirst(ZipFileData newFirstData) {
          String newFirstPath = newFirstData.path;
  
          Cell dupCell = cells.get(newFirstPath);
          if ( dupCell != null ) {
              throw new IllegalArgumentException("Path [ " + newFirstPath + " ] is already stored");
          }
  
          Cell oldFirstCell = anchor.next;
  
          Cell newFirstCell = new Cell(newFirstData);
          cells.put(newFirstPath, newFirstCell);
  
          newFirstCell.putBetween(anchor, oldFirstCell);
  
          return oldFirstCell.data;
      }