return when kafkaconsumer metrics are null

Author: jfzunigac

psc/src/main/java/com/pinterest/psc/consumer/kafka/PscKafkaConsumer.java

@@ -107,7 +107,8 @@ public void initializeBackend(ServiceDiscoveryConfig discoveryConfig, TopicUri t
 
     @Override
     protected synchronized void reportConsumerMetrics() {
-        if (kafkaConsumer == null)
+        // temporary fix to avoid NPE in KafkaConsumer.metrics()
+        if (kafkaConsumer == null || kafkaConsumer.metrics() == null)
             return;
 
         Map<org.apache.kafka.common.MetricName, ? extends org.apache.kafka.common.Metric> kafkaMetrics = kafkaConsumer.metrics();