code: protected static void checkSource(Configuration conf, List<Path> srcs
        ) throws InvalidInputException {
      List<IOException> ioes = new ArrayList<IOException>();
      for(Path p : srcs) {
        try {
          if (!p.getFileSystem(conf).exists(p)) {
            ioes.add(new FileNotFoundException("Source "+p+" does not exist."));
          }
        }
        catch(IOException e) {ioes.add(e);}
      }
      if (!ioes.isEmpty()) {
        throw new InvalidInputException(ioes);
      }
    }
docs: Sanity check for source