code: public File getModifiedFile(int index) {
      CheckUtilities.checkIntIndexInListRange(modifiedFiles, index);
      return modifiedFiles.get(index);
    }
docs: Returns the file at a given location in the modifiedFiles list.
  
  @param index
  in the list and it should be positive and less than total no. of files modified.
  @return modified file at the index in modifiedFiles list.