private void addToMetricsMessage(String groupName, String metricName, Object value) {
    if (value != null) {
      metricsMessage.putIfAbsent(groupName, new HashMap<>());
      metricsMessage.get(groupName).put(metricName, value);
    }
  }
Helper method to use {@link SamzaObjectMapper} to deserialize {@link ContainerModel}s.
{@link SamzaObjectMapper} provides several conventions and optimizations for deserializing containerModels.
@return
samza-core/src/main/scala/org/apache/samza/diagnostics/DiagnosticsStreamMessage.java