public void isEmpty() {
    if (actual == null) {
      failWithActual(simpleFact("expected an empty string"));
    } else if (!actual.isEmpty()) {
      failWithActual(simpleFact("expected to be empty"));
    }
  }
@Test
  public void stringIsEmptyFailNull() {
    expectFailureWhenTestingThat(null).isEmpty();
    assertFailureKeys("expected an empty string", "but was");
  }