Polish "Fix NullPointer when requesting a session that does not exist"

Closes gh-11202

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/session/SessionsEndpointTests.java

@@ -81,6 +81,12 @@ public class SessionsEndpointTests {
 		assertThat(result.isExpired()).isEqualTo(session.isExpired());
 	}
 
+	@Test
+	public void getSessionWithIdNotFound() {
+		given(this.repository.findById("not-found")).willReturn(null);
+		assertThat(this.endpoint.getSession("not-found")).isNull();
+	}
+
 	@Test
 	public void deleteSession() {
 		this.endpoint.deleteSession(session.getId());

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/session/SessionsEndpointWebIntegrationTests.java

@@ -82,8 +82,10 @@ public class SessionsEndpointWebIntegrationTests {
 
 	@Test
 	public void sessionForIdNotFound() {
-		client.get().uri((builder) -> builder.path("/actuator/sessions/some-session-id-that-does-not-exist")
-										.build()).exchange().expectStatus().isNotFound();
+		client.get()
+				.uri((builder) -> builder.path(
+						"/actuator/sessions/session-id-not-found").build())
+				.exchange().expectStatus().isNotFound();
 	}
 
 	@Configuration