@CollectionFeature.Require(absent = ALLOWS_NULL_VALUES)
  public void testAddAtIndex_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> getList().add(0, null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(n, null)");
  }

  @ListFeature.Require(SUPPORTS_ADD_WITH_INDEX)
  public void testAddAtIndex_negative() {

  public void testAdd_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> collection.add(null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(null)");
  }

  @CollectionFeature.Require({SUPPORTS_ADD, FAILS_FAST_ON_CONCURRENT_MODIFICATION})
  @CollectionSize.Require(absent = ZERO)

  public void testAdd_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> collection.add(null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(null)");
  }

  @CollectionFeature.Require({SUPPORTS_ADD, FAILS_FAST_ON_CONCURRENT_MODIFICATION})
  @CollectionSize.Require(absent = ZERO)

   * to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullMissingWhenNullUnsupported(String message) {
    try {
      assertFalse(message, actualContents().contains(null));
    } catch (NullPointerException tolerated) {
      // Tolerated
    }
  }

  public void testAddAll_nullUnsupported() {
    List<E> containsNull = singletonList(null);
    assertThrows(NullPointerException.class, () -> collection.addAll(containsNull));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported(
        "Should not contain null after unsupported addAll(containsNull)");
  }

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testAddAll_nullCollectionReference() {

  @CollectionFeature.Require(absent = ALLOWS_NULL_VALUES)
  public void testAddAtIndex_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> getList().add(0, null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported add(n, null)");
  }

  @ListFeature.Require(SUPPORTS_ADD_WITH_INDEX)
  public void testAddAtIndex_negative() {