Collection<@Nullable String> c = MinimalCollection.of("a", null, "b");
    try {
      copyOf((Collection<String>) c);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  enum TestEnum {
    A,
    B,
    C,
    D
  }

  public void testCopyOf_collection_enumSet() {
    Collection<TestEnum> c = EnumSet.of(TestEnum.A, TestEnum.B, TestEnum.D);

    Collection<@Nullable String> c = MinimalCollection.of("a", null, "b");
    try {
      copyOf((Collection<String>) c);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  enum TestEnum {
    A,
    B,
    C,
    D
  }

  public void testCopyOf_collection_enumSet() {
    Collection<TestEnum> c = EnumSet.of(TestEnum.A, TestEnum.B, TestEnum.D);