docs: private static int lastIndexOf(Object o, Object[] elements, int index) {
          if (o == null) {
              for (int i = index; i >= 0; i--)
                  if (elements[i] == null)
                      return i;
          } else {
              for (int i = index; i >= 0; i--)
                  if (o.equals(elements[i]))
                      return i;
          }
          return -1;
      }