Fix: resolve NPE with empty configMap setup for openstacktelemetry

Change-Id: Ib3f50f34845ddc631a928a037810e1fa688fa669
diff --git a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultPrometheusTelemetryConfig.java b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultPrometheusTelemetryConfig.java
index b22f053..33d1d2e 100644
--- a/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultPrometheusTelemetryConfig.java
+++ b/apps/openstacktelemetry/app/src/main/java/org/onosproject/openstacktelemetry/config/DefaultPrometheusTelemetryConfig.java
@@ -124,7 +124,6 @@
         @Override
         public PrometheusTelemetryConfig build() {
             checkNotNull(address, "Prometheus exporter binding address cannot be null");
-            checkNotNull(configMap, "Config map cannot be null");
             return new DefaultPrometheusTelemetryConfig(address, port, configMap);
         }
     }