code: def add_nullable_boolean_argument(parser, name, default=None, help_=None):
      
      group = parser.add_mutually_exclusive_group()
      group.add_argument(
          '--' + name, nargs='?', default=default, const=True, type=_str_to_bool,
          help=help_)
      group.add_argument('--no' + name, dest=name, action='store_false',
                         help=help_)
docs: Add a boolean argument to an ArgumentParser instance.