fix push notification delivery on android

backend/src/main/java/dev/ksan/etfoglasiserver/service/NotificationService.java

@@ -24,8 +24,20 @@ public class NotificationService {
 
         for (DeviceToken token : tokens) {
 
+            // Include a notification block so Android's system tray displays it
+            // even when the app is killed/dozing (a data-only message is only
+            // ever shown by the app's own JS handler, which won't run when the
+            // OS has force-stopped the app). HIGH priority tells FCM to deliver
+            // promptly and wake the device out of Doze.
             Message message = Message.builder()
                     .setToken(token.getFcmToken())
+                    .setNotification(Notification.builder()
+                            .setTitle(title)
+                            .setBody(body)
+                            .build())
+                    .setAndroidConfig(AndroidConfig.builder()
+                            .setPriority(AndroidConfig.Priority.HIGH)
+                            .build())
                     .putData("title", title)
                     .putData("body", body)
                     .build();

backend/src/main/java/dev/ksan/etfoglasiserver/service/SubjectService.java

@@ -74,6 +74,11 @@ public class SubjectService {
   @Async
   public void notifyAsync(Entry entry) {
 
+    // The scraper couldn't always match an announcement to a known subject, in
+    // which case there's nobody to notify. Guard against the NPE that would
+    // otherwise be thrown (and silently swallowed) on this async thread.
+    if (entry.getSubject() == null) return;
+
     List<User> users =
             userService.findUsersBySubjectId(entry.getSubject().getId());