Represent the list of "inner_type" objects in Gremlin form.

def _safe_gremlin_list(inner_type, argument_value):
    """Represent the list of "inner_type" objects in Gremlin form."""
    if not isinstance(argument_value, list):
        raise GraphQLInvalidArgumentError(u'Attempting to represent a non-list as a list: '
                                          u'{}'.format(argument_value))

    stripped_type = strip_non_null_from_type(inner_type)
    components = (
        _safe_gremlin_argument(stripped_type, x)
        for x in argument_value
    )
    return u'[' + u','.join(components) + u']'