private Object getFromMetricsMessage(String groupName, String metricName) {
    if (metricsMessage.containsKey(groupName) && metricsMessage.get(groupName) != null) {
      return metricsMessage.get(groupName).get(metricName);
    } else {
      return null;
    }
  }
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