最近，Android设备有时会抛出错误消息并崩溃：

java.lang.NullPointerException: 
  at com.happycenter.happycan.android.MyFirebaseInstanceIDService.a (Unknown Source:39)
  at com.google.firebase.iid.FirebaseInstanceIdService.b (Unknown Source:12)
  at com.google.firebase.iid.i.run (Unknown Source:24)
  at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1162)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:636)
  at java.lang.Thread.run (Thread.java:764)[/code]

它显然与Firebase有关。

我有时会在PlayStore面板中看到此报告。

我的依赖：

com.android.tools.build： g radle：3.4.2

com.google. gm s：google-services：3.2.0

com.google.火力基地：火力基地-信息： 11.8.0

buildToolsVersion 28.0.3

compileSdkVersion 28

minSdkVersion 14

TaretSdkVersion 28

源代码：

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.files.FileHandle;
import com.google.firebase.iid.FirebaseInstanceId;
import com.google.firebase.iid.FirebaseInstanceIdService;

public class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {

    @Override
    public void onTokenRefresh() {
        String token = FirebaseInstanceId.getInstance().getToken();
        registerToken(token);
    }

    private void registerToken(String token){
        FileHandle file;
        file = Gdx.files.local("data/t.txt");
        file.writeString(token, false);
    }
}

这个问题背后的原因是什么，我该如何解决？