code: public InputStream getStreamArgument(String name) throws JournalException {
          checkOpen();
          File file = (File) arguments.get(name);
          if (file == null) {
              return null;
          } else {
              try {
                  return new FileInputStream(file);
              } catch (FileNotFoundException e) {
                  throw new JournalException(e);
              }
          }
      }
docs: If they ask for an InputStream argument, get the File from the arguments
  map and create an InputStream on that file. If the value from the map is
  null, return null.