消息返回为未定义

Question

当数据存储在我的firebase数据库中时，我尝试通过firebase函数发送通知。它发送的消息没有问题，但我添加了一个日志标记，看看它是否上传到我的firebase数据库的文件的名称又回来了＃34;上传的讲义是： undefined ＆＃ 34 ;.那个第12行我不明白为什么。 以下是我的代码。

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initializeApp();

exports.sendNotification = functions.database.ref('/Lecture_Materials/{MIS}/{MISId}/name')
.onWrite(( change,context) =>{

// Grab the current value of what was written to the Realtime Database.
var eventSnapshot = change.after.val();
var str1 = "Lecture material uploaded is: " + eventSnapshot.name;
console.log(str1);

var topic = "Management.Information.System";
var payload = {
    data: {
        name: str1,
    }
};

// Send a message to devices subscribed to the provided topic.
return admin.messaging().sendToTopic(topic, payload)
    .then(function (response) {
        // See the MessagingTopicResponse reference documentation for the
        // contents of response.
        console.log("Successfully sent message:", response);
        return;
    })
    .catch(function (error) {
        console.log("Error sending message:", error);
    });
    });