func (l List) NewError(text string) Error {
	e := newError(nil, nil, text)
	e.list = l
	return e
}
func (l List) NewError(text string) Error {
	e := newError(nil, nil, text)
	e.list = l
	return e
}
// NewError returns an error with the given message and a list of
// key/value pairs copied from the list.