从Firebase实时数据库中获取无效和有效文档删除中的[空响应]

Question

此代码在dialogflow内联编辑器的webhook填充中。我给出的票证有效还是无效，我都没有在输出屏幕上得到答复。但是对于正确的票号，我可以将其删除，但无法向用户显示响应。

function delete(agent) {
    let message=" ";
    let usersRef = admin.database().ref('user/'+tick);

    usersRef.orderByValue().on("value", function(snapshot) {
        console.log(snapshot.val());

        if (snapshot.exists()) {
            message = " Your Appointment is been cancelled";// This message i 
            // want to show for successful deletion to the user.
            console.log("Deleted");
            usersRef.remove();
        } else {
            console.log("Not Deleted");
            message = " Invalid ticket number!! Please provide a valid one.";
        }
    });

    agent.add(tick+ message);
}