code: private final RequestMetricCollector findRequestMetricCollector(
              RequestMetricCollector reqLevelMetricsCollector) {
  
          RequestMetricCollector requestMetricCollector;
  
          if (reqLevelMetricsCollector != null) {
              requestMetricCollector = reqLevelMetricsCollector;
          } else if (getRequestMetricsCollector() != null) {
              requestMetricCollector =  getRequestMetricsCollector();
          } else {
              requestMetricCollector = AwsSdkMetrics.getRequestMetricCollector();
          }
          return requestMetricCollector;
      }
docs: Returns the most specific request metric collector, starting from the request level, then
  client level, then finally the AWS SDK level.