*
     * @return this tester
     */
    @CanIgnoreReturnValue
    public FactoryMethodReturnValueTester testNulls() throws Exception {
      for (Invokable<?, ?> factory : getFactoriesToTest()) {
        Object instance = instantiate(factory);
        if (instance != null
            && packagesToTest.contains(Reflection.getPackageName(instance.getClass()))) {
          try {