[GOBBLIN-2059] Send empty resource if no custom configs are specified (#3939)

* Send empty resource if no custom configs are specified

Author: Will-Lo

gobblin-metrics-libs/gobblin-metrics/src/main/java/org/apache/gobblin/metrics/OpenTelemetryMetrics.java

@@ -86,12 +86,17 @@ protected void initialize(State state) {
     log.info("Initializing OpenTelemetry metrics");
     Properties metricProps = PropertiesUtils.extractChildProperties(state.getProperties(),
         ConfigurationKeys.METRICS_REPORTING_OPENTELEMETRY_CONFIGS_PREFIX);
-    AttributesBuilder attributesBuilder = Attributes.builder();
-    for (String key : metricProps.stringPropertyNames()) {
-      attributesBuilder.put(AttributeKey.stringKey(key), metricProps.getProperty(key));
+    // Default to empty resource because default resource still populates some values
+    Resource metricsResource = Resource.empty();
+    if (metricProps.isEmpty()) {
+      log.warn("No OpenTelemetry metrics properties found, sending empty resource");
+    } else {
+      AttributesBuilder attributesBuilder = Attributes.builder();
+      for (String key : metricProps.stringPropertyNames()) {
+        attributesBuilder.put(AttributeKey.stringKey(key), metricProps.getProperty(key));
+      }
+      metricsResource = Resource.getDefault().merge(Resource.create(attributesBuilder.build()));
     }
-    Resource metricsResource = Resource.getDefault().merge(Resource.create(attributesBuilder.build()));
-
     SdkMeterProvider meterProvider = SdkMeterProvider.builder()
         .setResource(metricsResource)
         .registerMetricReader(