Merge branch '4.0.x'

Closes gh-50790

Author: bclozel

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