code: @Override
      public OptionalThing<String> getParameter(String key) {
          assertArgumentNotNull("key", key);
          final String param = getRequest().getParameter(key);
          return OptionalThing.ofNullable(param != null && !param.isEmpty() ? param : null, () -> {
              throw new IllegalStateException("Not found the request parameter for the key: " + key);
          });
      }
docs: ==================