assertThrows(IllegalArgumentException.class, () -> checkArgument(false, null));
    assertThat(expected).hasMessageThat().isEqualTo("null");
  }

  public void testCheckArgument_nullMessageWithArgs_failure() {
    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> checkArgument(false, null, "b", "d"));
    assertThat(e).hasMessageThat().isEqualTo("null [b, d]");
  }