code: public final void process(final File file) {
          if (file == null) {
              throw new IllegalArgumentException("Argument 'file' cannot be NULL");
          }
          if (file.isFile()) {
              handler.handleFile(file);
          } else {
              processDir(file);
          }
      }
docs: Processes a file or directory.
  
  @param file
  File - Cannot be NULL.