code: public static <T> CloseableIterator<T> concat(final CloseableIterator<? extends Iterator<? extends T>> iterators) {
          return wrap(Iterators.concat(iterators), iterators);
      }
docs: Combines multiple iterators into a single closeable iterator. The returned
  closeable iterator iterates across the elements of each iterator in {@code inputs}.
  The input iterators are not polled until necessary.