Only set Partitioned cookie attribute when true

The session cookie's Partitioned attribute was set to "" for any
non-null value, so an explicit `partitioned=false` was rendered the
same as `true`. PropertyMapper.to() only filters null, so
Boolean.FALSE reached the consumer and the attribute was always set.

Use whenTrue() so the attribute is set only when partitioned is true,
leaving false and unset to fall through to the container default.

Signed-off-by: Lee JiWon <dlwldnjs1009@gmail.com>

Author: dlwldnjs1009

module/spring-boot-web-server/src/main/java/org/springframework/boot/web/server/servlet/ServletContextInitializers.java

@@ -97,7 +97,7 @@ private void configureSessionCookie(SessionCookieConfig config) {
 			map.from(cookie::getHttpOnly).to(config::setHttpOnly);
 			map.from(cookie::getSecure).to(config::setSecure);
 			map.from(cookie::getMaxAge).asInt(Duration::getSeconds).to(config::setMaxAge);
-			map.from(cookie::getPartitioned).to((partitioned) -> config.setAttribute("Partitioned", ""));
+			map.from(cookie::getPartitioned).whenTrue().to((partitioned) -> config.setAttribute("Partitioned", ""));
 		}
 
 		@Contract("!null -> !null")

module/spring-boot-web-server/src/testFixtures/java/org/springframework/boot/web/server/servlet/AbstractServletWebServerFactoryTests.java

@@ -899,6 +899,20 @@ void sessionCookiePartitionedAttribute() throws Exception {
 				(header) -> assertThat(header).isEqualTo("test=test"));
 	}
 
+	@Test
+	void sessionCookieNotPartitionedAttribute() throws Exception {
+		ConfigurableServletWebServerFactory factory = getFactory();
+		factory.getSettings().getSession().getCookie().setPartitioned(false);
+		factory.addInitializers(new ServletRegistrationBean<>(new CookieServlet(false), "/"));
+		this.webServer = factory.getWebServer();
+		this.webServer.start();
+		ClientHttpResponse clientResponse = getClientResponse(getLocalUrl("/"));
+		List<String> setCookieHeaders = clientResponse.getHeaders().get("Set-Cookie");
+		assertThat(setCookieHeaders).satisfiesExactlyInAnyOrder(
+				(header) -> assertThat(header).startsWith("JSESSIONID=").doesNotContain("; Partitioned"),
+				(header) -> assertThat(header).isEqualTo("test=test"));
+	}
+
 	@ParameterizedTest
 	@EnumSource(mode = EnumSource.Mode.EXCLUDE, names = "OMITTED")
 	void sessionCookieSameSiteAttributeCanBeConfiguredAndOnlyAffectsSessionCookies(SameSite sameSite) throws Exception {
@@ -1226,7 +1240,7 @@ void sessionConfiguration() {
 		assertThat(sessionCookieConfig.isHttpOnly()).isTrue();
 		assertThat(sessionCookieConfig.isSecure()).isTrue();
 		assertThat(sessionCookieConfig.getMaxAge()).isEqualTo(60);
-		assertThat(sessionCookieConfig.getAttribute("Partitioned")).isEqualTo("");
+		assertThat(sessionCookieConfig.getAttribute("Partitioned")).isNull();
 	}
 
 	@Test