code: public JsonElement getLowWatermark() {
      if (!contains(ConfigurationKeys.WATERMARK_INTERVAL_VALUE_KEY)) {
        return null;
      }
      return JSON_PARSER.parse(getProp(ConfigurationKeys.WATERMARK_INTERVAL_VALUE_KEY)).getAsJsonObject()
          .get(WatermarkInterval.LOW_WATERMARK_TO_JSON_KEY);
    }
docs: Get the low {@link Watermark} as a {@link JsonElement}.
  
  @return a {@link JsonElement} representing the low {@link Watermark} or
  {@code null} if the low {@link Watermark} is not set.