Firebase Admin SDK(Java)を使った、Cloud Messagingを組み込んだServletがエラーを返す

こんにちは。
サーバにtomcatを入れて、Firebase Admin SDK(Java)を使った、Cloud Messagingを組み込んだServletを仕込んで、localhostからPostとしようとしています。

https://firebase.google.com/docs/admin/setup
https://firebase.google.com/docs/cloud-messaging/send-message?hl=ja
を参照して以下のコードを書きましたが、

HTTP Status 500 – Internal Server Error

Type Exception Report

Message Servlet execution threw an exception

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

javax.servlet.ServletException: Servlet execution threw an exception
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Root Cause

java.lang.NoSuchMethodError: com.google.common.primitives.Booleans.countTrue([Z)I
com.google.firebase.messaging.Message.<init>(Message.java:72)
com.google.firebase.messaging.Message.<init>(Message.java:40)
com.google.firebase.messaging.Message$Builder.build(Message.java:276)
App.doPost(App.java:32)
javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Note The full stack trace of the root cause is available in the server logs.
Apache Tomcat/7.0.92

こういうエラーが出ます。
困っています。そもそもコードは合っているんでしょうか？解決のお手伝いをよろしくお願いします。

途中の変数をtoString()をしてみました。参考にして下さい。

GoogleCredentials.fromStream(serviceAccount)の返り値：
ServiceAccountCredentials{clientId=xxx, clientEmail=firebase-adminsdk-y8p0y@xxx.iam.gserviceaccount.com, privateKeyId=xxx, transportFactoryClassName=com.google.auth.oauth2.OAuth2Utils$DefaultHttpTransportFactory, tokenServerUri=https://oauth2.googleapis.com/token, scopes=[], serviceAccountUser=null}

FirebaseOptions options:
com.google.firebase.FirebaseOptions@xxx

Java
1import java.io.*;
2import javax.servlet.*;
3import javax.servlet.http.*;
4import com.google.firebase.*;
5import com.google.firebase.messaging.*;
6import com.google.auth.oauth2.GoogleCredentials;
7
8public class App extends HttpServlet {
9  public void doPost (HttpServletRequest req, HttpServletResponse res)
10    throws ServletException, IOException{
11    PrintWriter out;
12
13    res.setContentType("text/plain; charset=utf-8");
14    out = res.getWriter();
15
16    FileInputStream serviceAccount = new FileInputStream("xxx.json");
17
18    FirebaseOptions options = new FirebaseOptions.Builder()
19    .setCredentials(GoogleCredentials.fromStream(serviceAccount))
20    .setDatabaseUrl("https://xxx.firebaseio.com")
21    .build();
22
23    FirebaseApp.initializeApp(options);
24
25    String deviceToken="xxx";
26    Message message = Message.builder()
27    .putData("score", "850")
28    .putData("time", "2:45")
29    .setToken(deviceToken)
30    .build();
31
32     String response="";
33     try{
34        response = FirebaseMessaging.getInstance().send(message);
35     }
36     catch(Exception e){
37     }
38     out.println("Successfully sent message: " + response);
39  }
40}

Gradle
1apply plugin: 'java'
2repositories {
3    mavenCentral()
4    jcenter()
5}
6
7dependencies {
8    // The production code uses the SLF4J logging API at compile time
9    compile 'org.slf4j:slf4j-api:1.7.21'
10    compile 'javax.servlet:javax.servlet-api:3.1.0'
11    compile 'com.google.firebase:firebase-admin:6.8.0'
12    compile 'com.google.apis:google-api-services-oauth2:v1-rev154-1.25.0'
13    testCompile 'junit:junit:4.12'
14}