input.put(null, 1);
    assertThrows(
        NullPointerException.class,
        () -> ImmutableListMultimap.copyOf((ArrayListMultimap<String, Integer>) input));
  }

  public void testCopyOfNullValue() {
    ArrayListMultimap<String, @Nullable Integer> input = ArrayListMultimap.create();
    input.putAll("foo", Arrays.<@Nullable Integer>asList(1, null, 3));
    assertThrows(
        NullPointerException.class,