code: func NewMessagesSentTotalStatsHandler(sub Subsystem, vec *prometheus.CounterVec) *MessagesSentTotalStatsHandler {
  	return &MessagesSentTotalStatsHandler{
  		baseStatsHandler: baseStatsHandler{
  			subsystem: sub,
  			collector: vec,
  		},
  		vec: vec,
  	}
  }
docs: // NewMessagesSentTotalStatsHandler ...
  // The GaugeVec must have zero, one, two, three or four non-const non-curried labels.
  // For those, the only allowed label names are "fail_fast", "handler", "service" and "user_agent".