code: public <T extends Watermark> T getExpectedHighWatermark(Class<T> watermarkClass) {
      return getExpectedHighWatermark(watermarkClass, GSON);
    }
docs: Get the expected high {@link Watermark}. A default {@link Gson} object will be used to deserialize the watermark.
  
  @param watermarkClass the watermark class for this {@code WorkUnit}.
  @return the expected high watermark in this {@code WorkUnit}.