fix: NPE when web push subscription is expired (#24310) (CP: 25.1) (#24316)

This PR cherry-picks changes from the original PR #24310 to branch 25.1.
---
#### Original PR description
> When the push service reports a subscription as expired,
`WebPush.sendNotification` threw `NullPointerException` instead of the
intended `WebPushException`.
> 
> Remove a leftover reference to an unassigned `HttpResponse` local
variable that was no longer populated after the migration to
`com.interaso.webpush`.
> 
> Fixes #24306
>

Co-authored-by: Marco Collovati <marco@vaadin.com>

Author: vaadin-bot

flow-webpush/src/main/java/com/vaadin/flow/server/webpush/WebPush.java

@@ -18,7 +18,6 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.Serializable;
-import java.net.http.HttpResponse;
 import java.security.spec.InvalidKeySpecException;
 
 import com.interaso.webpush.VapidKeys;
@@ -108,8 +107,7 @@ public WebPush(String publicKey, String privateKey, String subject) {
      */
     public void sendNotification(WebPushSubscription subscription,
             WebPushMessage message) throws WebPushException {
-        SubscriptionState status = null;
-        HttpResponse<String> response = null;
+        SubscriptionState status;
         try {
             status = pushService.send(message.toJson(), subscription.endpoint(),
                     subscription.keys().p256dh(), subscription.keys().auth(),
@@ -122,7 +120,6 @@ public void sendNotification(WebPushSubscription subscription,
         if (!SubscriptionState.ACTIVE.equals(status)) {
             getLogger().error(
                     "Failed to send web push notification, received status code: 404 or 410");
-            getLogger().error(String.join("\n", response.body()));
             throw new WebPushException(
                     "Sending of web push notification failed with status code 404 or 410");
         }

flow-webpush/src/test/java/com/vaadin/flow/server/webpush/WebPushTest.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2000-2026 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.server.webpush;
+
+import java.lang.reflect.Field;
+
+import com.interaso.webpush.WebPush.SubscriptionState;
+import com.interaso.webpush.WebPushService;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class WebPushTest {
+
+    private static final String PUBLIC_KEY = "BPXZkCj3rxN6a1v21aCyMQHmTaAn1QZyWRDeBfwQ4qperQNszSD9JhnZv9b45vHLQLxnK3zsCvCl1r8EDpPDjoM";
+    private static final String PRIVATE_KEY = "W-J0f4QwsjrEwDnJJTky5waIX9xNaM87-Dfd42_SEDM";
+
+    private WebPush webPush;
+    private WebPushService pushServiceMock;
+
+    @Before
+    public void setUp() throws Exception {
+        webPush = new WebPush(PUBLIC_KEY, PRIVATE_KEY,
+                "mailto:test@example.com");
+        pushServiceMock = mock(WebPushService.class);
+        Field field = WebPush.class.getDeclaredField("pushService");
+        field.setAccessible(true);
+        field.set(webPush, pushServiceMock);
+    }
+
+    @Test
+    public void sendNotification_subscriptionExpired_throwsWebPushException() {
+        when(pushServiceMock.send(any(String.class), any(String.class),
+                any(String.class), any(String.class), any(), any(), any()))
+                .thenReturn(SubscriptionState.EXPIRED);
+
+        WebPushSubscription subscription = new WebPushSubscription(
+                "https://push.example/endpoint",
+                new WebPushKeys("p256dhKey", "authKey"));
+        WebPushMessage message = new WebPushMessage("title", "body");
+
+        WebPushException ex = assertThrows(WebPushException.class,
+                () -> webPush.sendNotification(subscription, message));
+        assertEquals(
+                "Sending of web push notification failed with status code 404 or 410",
+                ex.getMessage());
+    }
+
+    @Test
+    public void sendNotification_subscriptionActive_doesNotThrow() {
+        when(pushServiceMock.send(any(String.class), any(String.class),
+                any(String.class), any(String.class), any(), any(), any()))
+                .thenReturn(SubscriptionState.ACTIVE);
+
+        WebPushSubscription subscription = new WebPushSubscription(
+                "https://push.example/endpoint",
+                new WebPushKeys("p256dhKey", "authKey"));
+        WebPushMessage message = new WebPushMessage("title", "body");
+
+        webPush.sendNotification(subscription, message);
+    }
+}