code: public static void assertNull(String message, Object o) {
          if (o == null) {
              pass(message);
          } else {
              fail(message, "'" + o + "' is not null");
          }
      }
docs: Assert that a value is null.
  <p>
  If the assertion passes, a green tick will be shown. If the assertion fails, a red cross will be shown.
  
  @param message message to display alongside the assertion outcome
  @param o       value to test