docs: def set_system_conf(self, key=None, value=None, d=None):
          """ Sets a java system property as a ('key', 'value') pair of using a dictionary
          {'key': 'value', ...}
  
          :param key: string
          :param value: string
          :param d: dictionary
          :return: None
          """
          if isinstance(d, dict):
              self._system.update(d)
          elif isinstance(key, str) and isinstance(value, str):
              self._system[key] = value
          else:
              raise TypeError("key, value must be strings")