code: def add_compound(self, compound_stat, config=None):
          
          if not compound_stat:
              raise ValueError('compound stat must be non-empty')
          self._stats.append(compound_stat)
          for named_measurable in compound_stat.stats():
              metric = KafkaMetric(named_measurable.name, named_measurable.stat,
                                   config or self._config)
              self._registry.register_metric(metric)
              self._metrics.append(metric)
docs: Register a compound statistic with this sensor which
          yields multiple measurable quantities (like a histogram)
  
          Arguments:
              stat (AbstractCompoundStat): The stat to register
              config (MetricConfig): The configuration for this stat.
                  If None then the stat will use the default configuration
                  for this sensor.