public static ItemSpec<String> item(String key, @Nullable String value) {
    return item(key, Type.STRING, value);
  }
@Test
  public void testCanSerializeItemSpecReference() {
    DisplayData.ItemSpec<?> spec = DisplayData.item("clazz", DisplayDataTest.class);
    SerializableUtils.ensureSerializable(new HoldsItemSpecReference(spec));
  }