NullPointerException.class, () -> builder.put(immutableEntry("one", (Integer) null)));
    assertThrows(NullPointerException.class, () -> builder.put(immutableEntry((String) null, 1)));
  }

  public void testBuilderWithExpectedKeysNegative() {
    assertThrows(
        IllegalArgumentException.class, () -> ImmutableMultimap.builderWithExpectedKeys(-1));
  }

  public void testBuilderWithExpectedKeysZero() {