空对象引用上的'int java.lang.String.hashCode（）'

Question

我正在使用一个类通过Firebase消息发送我的通知，现在出现以下错误：

FATAL EXCEPTION: Firebase-NotifFirebaseMessagingService
              Process: com.safshari.iwallpaper, PID: 3325
              java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.hashCode()' on a null object reference
                  at com.safshari.iwallpaper.services.NotifFirebaseMessagingService.onMessageReceived(NotifFirebaseMessagingService.java:51)
                  at com.google.firebase.messaging.FirebaseMessagingService.zzd(Unknown Source)
                  at com.google.firebase.iid.zzc.run(Unknown Source)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
                  at com.google.android.gms.common.util.concurrent.zza.run(Unknown Source)
                  at java.lang.Thread.run(Thread.java:762)

这是我用来发送或接收消息的firebasee消息传递类：

public class NotifFirebaseMessagingService extends FirebaseMessagingService {

private static final String TAG = "FCM Service";
Bitmap bitmap;

@Override
public void onMessageReceived(RemoteMessage remoteMessage) {




    String type = remoteMessage.getData().get("type");
    String id = remoteMessage.getData().get("id");
    String title = remoteMessage.getData().get("title");
    String image = remoteMessage.getData().get("image");
    String icon = remoteMessage.getData().get("icon");
    String message = remoteMessage.getData().get("message");

    PrefManager prf = new PrefManager(getApplicationContext());
    if (!prf.getString("notifications").equals("false")) {

        switch (type) {
            case "wallpaper":

                String wallpaper_title = remoteMessage.getData().get("wallpaper_title");
                String wallpaper_size = remoteMessage.getData().get("wallpaper_size");
                String wallpaper_sets = remoteMessage.getData().get("wallpaper_sets");
                String wallpaper_review = remoteMessage.getData().get("wallpaper_review");
                String wallpaper_downloads = remoteMessage.getData().get("wallpaper_downloads");
                String wallpaper_resolution = remoteMessage.getData().get("wallpaper_resolution");
                String wallpaper_color = remoteMessage.getData().get("wallpaper_color");
                String wallpaper_user = remoteMessage.getData().get("wallpaper_user");
                String wallpaper_comment = remoteMessage.getData().get("wallpaper_comment");
                String wallpaper_type = remoteMessage.getData().get("wallpaper_type");
                String wallpaper_description = remoteMessage.getData().get("wallpaper_description");
                String wallpaper_extension = remoteMessage.getData().get("wallpaper_extension");
                String wallpaper_thumbnail = remoteMessage.getData().get("wallpaper_thumbnail");
                String wallpaper_image = remoteMessage.getData().get("wallpaper_image");
                String wallpaper_wallpaper = remoteMessage.getData().get("wallpaper_wallpaper");
                String wallpaper_userimage = remoteMessage.getData().get("wallpaper_userimage");
                String wallpaper_created = remoteMessage.getData().get("wallpaper_created");
                String wallpaper_comments = remoteMessage.getData().get("wallpaper_created");

                sendNotification(
                        id,
                        title,
                        image,
                        icon,
                        message,
                        wallpaper_title,
                        wallpaper_size,
                        wallpaper_sets,
                        wallpaper_review,
                        wallpaper_downloads,
                        wallpaper_resolution,
                        wallpaper_color,
                        wallpaper_user,
                        wallpaper_comment,
                        wallpaper_type,
                        wallpaper_extension,
                        wallpaper_thumbnail,
                        wallpaper_image,
                        wallpaper_wallpaper,
                        wallpaper_userimage,
                        wallpaper_created,
                        wallpaper_comments,
                        wallpaper_description
                );
                break;
            case "category":
                String category_title = remoteMessage.getData().get("title_category");
                String category_image = remoteMessage.getData().get("image_category");

                sendNotificationCategory(
                        id,
                        title,
                        image,
                        icon,
                        message,
                        category_title,
                        category_image);
                break;
            case "link":
                String link = remoteMessage.getData().get("link");

                sendNotificationUrl(
                        id,
                        title,
                        image,
                        icon,
                        message,
                        link
                );
                break;
        }
    }


}

实际上，它是我的Firebase消息传递类的一部分，整个类都在300行以上，在运行第51行之前发生错误，在此之前我曾经使用过if而不是switch case，但是我设法使用了switch case但我不认为相关。