code: public JsonObject getJsonObject(String name) throws JsonException {
          JsonElement el = get(name);
          if (!el.isJsonObject()) {
              throw Util.typeMismatch(name, el, "JsonObject");
          }
          return el.asJsonObject();
      }
docs: Returns the value mapped by {@code name} if it exists and is a {@code
  JsonObject}, or throws otherwise.
  
  @throws JsonException if the mapping doesn't exist or is not a {@code
  JsonObject}.