code: public JsonArray getJsonArray(int index) throws JsonException {
          JsonElement el = get(index);
          if (!el.isJsonArray()) {
              throw Util.typeMismatch(index, el, "JsonArray");
          }
          return el.asJsonArray();
      }
docs: Returns the value at {@code index} if it exists and is a {@code
  JsonArray}.
  
  @throws JsonException if the value doesn't exist or is not a {@code
  JsonArray}.