code: func (opts *UNSUBSCRIBEOptions) validate() error {
  	// Check the Packet Identifier.
  	if opts.PacketID == 0 {
  		return ErrInvalidPacketID
  	}
  
  	// Check the existence of the subscription requests.
  	if len(opts.TopicFilters) == 0 {
  		return ErrNoTopicFilter
  	}
  
  	// Check the Topic Filters.
  	for _, topicFilter := range opts.TopicFilters {
  		// Check the length of the Topic Filter.
  		l := len(topicFilter)
  
  		if l == 0 {
  			return ErrNoTopicFilter
  		}
  
  		if l > maxStringsLen {
  			return ErrTopicFilterExceedsMaxStringsLen
  		}
  	}
  
  	return nil
  }
docs: // validate validates the options.