Fix MapReactorSessionRepository's delete().

spring-session-core/src/main/java/org/springframework/session/MapReactorSessionRepository.java

@@ -123,17 +123,10 @@ private void performSave(MapSession session) {
 	}
 
 	public Mono<MapSession> findById(String id) {
-		return Mono.defer(() -> {
-			Session saved = this.sessions.get(id);
-			if (saved == null) {
-				return Mono.empty();
-			}
-			if (saved.isExpired()) {
-				delete(saved.getId());
-				return Mono.empty();
-			}
-			return Mono.just(new MapSession(saved));
-		});
+		return Mono.defer(() -> Mono.justOrEmpty(this.sessions.get(id))
+			.filter(session -> !session.isExpired())
+			.map(MapSession::new)
+			.switchIfEmpty(delete(id).then(Mono.empty())));
 	}
 
 	public Mono<Void> delete(String id) {

spring-session-core/src/test/java/org/springframework/session/MapReactorSessionRepositoryTests.java

@@ -22,6 +22,7 @@
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -33,6 +34,7 @@
  * @since 2.0
  */
 public class MapReactorSessionRepositoryTests {
+
 	MapReactorSessionRepository repository;
 
 	MapSession session;
@@ -124,6 +126,19 @@ public void findByIdWhenExpiredThenEmpty() {
 		assertThat(this.repository.findById(this.session.getId()).block()).isNull();
 	}
 
+	@Test
+	public void findByIdWhenExpiredRemovesFromSessionMap() {
+		this.session.setMaxInactiveInterval(Duration.ofMinutes(1));
+		this.session.setLastAccessedTime(Instant.now().minus(5, ChronoUnit.MINUTES));
+
+		Map<String, Session> sessions = new ConcurrentHashMap<>();
+		sessions.put("session-id", this.session);
+		this.repository = new MapReactorSessionRepository(sessions);
+
+		assertThat(this.repository.findById(this.session.getId()).block()).isNull();
+		assertThat(sessions).isEmpty();
+	}
+
 	@Test
 	public void createSessionWhenDefaultMaxInactiveIntervalThenDefaultMaxInactiveInterval() {
 		Session session = this.repository.createSession().block();