code: public void assertNullOrEmpty(Description description, Set<?> actual) {
      if (actual == null || actual.isEmpty()) {
        return;
      }
      throw failures.failure(description, shouldBeNullOrEmpty(actual));
    }
docs: Asserts that the given <code>{@link Set}</code> is {@code null} or empty.
  
  @param description contains information about the assertion.
  @param actual the given {@code Set}.
  @throws AssertionError if the given {@code Set} is not {@code null} *and* contains one or more elements.