public void addMetric(MetricName metricName, Measurable measurable) {
        addMetric(metricName, null, measurable);
    }
Add a metric to monitor an object that implements measurable. This metric won't be associated with any sensor.
This is a way to expose existing values as metrics.

This method is kept for binary compatibility purposes, it has the same behaviour as
{@link #addMetric(MetricName, MetricValueProvider)}.

@param metricName The name of the metric
@param measurable The measurable that will be measured by this metric
clients/src/main/java/org/apache/kafka/common/metrics/Metrics.java