pubsub.go
func WithBlacklist(b Blacklist) Option {
	return func(p *PubSub) error {
		p.blacklist = b
		return nil
	}
}
func WithBlacklist(b Blacklist) Option {
	return func(p *PubSub) error {
		p.blacklist = b
		return nil
	}
}
// WithBlacklist provides an implementation of the blacklist; the default is a
// MapBlacklist