public void testNullPointerExceptions() {
    NullPointerTester tester = new NullPointerTester();
    tester.testAllPublicStaticMethods(Collections2.class);
  }

  public void testOrderedPermutationSetEmpty() {
    List<Integer> list = new ArrayList<>();
    Collection<List<Integer>> permutationSet = Collections2.orderedPermutations(list);

    assertEquals(1, permutationSet.size());