code: def get_option_default(self, key, subkey):
          
          key, subkey = _lower_keys(key, subkey)
          _entry_must_exist(self.gc, key, subkey)
  
          df = self.gc[(self.gc["k1"] == key) & (self.gc["k2"] == subkey)]
          if df["type"].values[0] == "bool":
              return bool(df["default"].values[0])
          elif df["type"].values[0] == "int":
              return int(df["default"].values[0])
          else:
              return df["default"].values[0]
docs: Get the default value of the option.
  
          :param str key: First identifier of the option.
          :param str subkey: Second identifier of the option.
  
          :return: Default value of the option (type varies).
  
          :raise:
              :NotRegisteredError: If ``key`` or ``subkey`` do not define
                  any option.