code: public void assertIsSorted(Description description, char[] actual) {
      if(actual == null) {
        throw failures.failure("The actual is null");
      }
      if (actual.length == 0) {
        return;
      }
      for (int i = 0; i < actual.length - 1; i++) {
        if (actual[i] > actual[i + 1]) {
          throw failures.failure(description, shouldBeSorted(i, actual));
        }
      }
    }
docs: Verifies that the actual is sorted into ascending order according to the natural ordering of its elements.
  Empty arrays are considered sorted.
  
  @param description contains the information about the assertion.
  @param actual the given array.
  @throws AssertionError if the {@code actual} is {@code null}.