Remove parent observation key instead of setting null.

When completing a MongoObservation without a parent observation, we now remove the parent observation key from the request context instead of setting it to null.

In reactive usage, the context map is a ConcurrentHashMap that does not allow null values.

Closes #5082
Original pull request #5083

Author: mp911de

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/observability/MongoObservationCommandListener.java

@@ -17,6 +17,7 @@
 
 import io.micrometer.observation.Observation;
 import io.micrometer.observation.ObservationRegistry;
+import io.micrometer.observation.ObservationView;
 import io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor;
 
 import java.util.function.BiConsumer;
@@ -191,7 +192,13 @@ private void stopObservation(@Nullable RequestContext requestContext,
 				log.debug(
 						"Restoring parent observation [" + observation + "] for Mongo instrumentation and put it in Mongo context");
 			}
-			requestContext.put(ObservationThreadLocalAccessor.KEY, observation.getContext().getParentObservation());
+			ObservationView parentObservation = observation.getContext().getParentObservation();
+
+			if (parentObservation == null) {
+				requestContext.delete(ObservationThreadLocalAccessor.KEY);
+			} else {
+				requestContext.put(ObservationThreadLocalAccessor.KEY, parentObservation);
+			}
 		}
 	}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/observability/MongoObservationCommandListenerTests.java

@@ -26,6 +26,7 @@
 import io.micrometer.observation.Observation;
 import io.micrometer.observation.ObservationRegistry;
 import io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor;
+import reactor.core.publisher.BaseSubscriber;
 
 import org.assertj.core.api.Assertions;
 import org.bson.BsonDocument;
@@ -43,6 +44,7 @@
 import com.mongodb.event.CommandFailedEvent;
 import com.mongodb.event.CommandStartedEvent;
 import com.mongodb.event.CommandSucceededEvent;
+import com.mongodb.reactivestreams.client.ReactiveContextProvider;
 
 /**
  * Series of test cases exercising {@link MongoObservationCommandListener}.
@@ -113,6 +115,25 @@ void commandStartedShouldAlwaysIncludeCollection() {
 				Tags.of("db.mongodb.collection", "none"));
 	}
 
+	@Test // GH-5082
+	void reactiveContextCompletesNormally() {
+
+		ReactiveContextProvider rcp = (ReactiveContextProvider) ContextProviderFactory.create(observationRegistry);
+		RequestContext context = rcp.getContext(new BaseSubscriber<>() {});
+
+		listener.commandStarted(new CommandStartedEvent(context, 0, 0, //
+				new ConnectionDescription( //
+						new ServerId( //
+								new ClusterId("description"), //
+								new ServerAddress("localhost", 1234))),
+				"database", "insert", //
+				new BsonDocument("collection", new BsonString("user"))));
+		listener.commandSucceeded(new CommandSucceededEvent(context, 0, 0, null, "insert", null, null, 0));
+
+		// then
+		assertThatTimerRegisteredWithTags();
+	}
+
 	@Test
 	void successfullyCompletedCommandShouldCreateTimerWhenParentSampleInRequestContext() {