public void testNulls_interface() {
    tester.testNulls(AnInterface.class);
  }

  public void testNulls_abstractClass() {
    tester.testNulls(AnAbstractClass.class);
  }

  public void testNulls_enum() throws Exception {
    tester.testNulls(OneConstantEnum.class);
    tester.testNulls(NoConstantEnum.class);
    tester.testNulls(TimeUnit.class);
  }