code: def emit(self, view_data):  # pragma: NO COVER
          
  
          for v_data in view_data:
              if v_data.tag_value_aggregation_data_map:
                  self.collector.add_view_data(v_data)
docs: Emit exports to the Prometheus if view data has one or more rows.
          Each OpenCensus AggregationData will be converted to
          corresponding Prometheus Metric: SumData will be converted
          to Untyped Metric, CountData will be a Counter Metric
          DistributionData will be a Histogram Metric.