public final void isEmpty() {
    if (!Iterables.isEmpty(checkNotNull(actual))) {
      failWithActual(simpleFact("expected to be empty"));
    }
  }
@Test
  public void iterableIsEmptyWithFailure() {
    expectFailureWhenTestingThat(asList(1, null, 3)).isEmpty();
    assertFailureKeys("expected to be empty", "but was");
  }