升级到 Null Safety 后，sdk: ">=2.12.0 <3.0.0"当我尝试在 Android Studio 中构建 Flutter 应用程序时出现错误。

C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:20: error: cannot find symbol
    import com.google.firebase.iid.FirebaseInstanceId;
                                  ^
      symbol:   class FirebaseInstanceId
      location: package com.google.firebase.iid
    C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:21: error: cannot find symbol
    import com.google.firebase.iid.Metadata;
                                  ^
      symbol:   class Metadata
      location: package com.google.firebase.iid
    C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:152: error: cannot find symbol
                      : Metadata.getDefaultSenderId(FirebaseApp.getInstance());
                        ^
      symbol:   variable Metadata
      location: class FlutterFirebaseMessagingPlugin
    C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:153: error: cannot find symbol
              FirebaseInstanceId.getInstance().deleteToken(senderId, "*");
              ^
      symbol:   variable FirebaseInstanceId
      location: class FlutterFirebaseMessagingPlugin
    C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:165: error: cannot find symbol
                      : Metadata.getDefaultSenderId(FirebaseApp.getInstance());
                        ^
      symbol:   variable Metadata
      location: class FlutterFirebaseMessagingPlugin
    C:flutter.pub-cachehostedpub.dartlang.orgfirebase_messaging-9.1.4androidsrcmainjavaioflutterpluginsfirebasemessagingFlutterFirebaseMessagingPlugin.java:166: error: cannot find symbol
              String token = FirebaseInstanceId.getInstance().getToken(senderId, "*");
                             ^
      symbol:   variable FirebaseInstanceId
      location: class FlutterFirebaseMessagingPlugin

Android Studio 告诉我 FlutterFirebaseMessagingPlugin.java“找不到符号”。那么这是什么意思，我该如何解决

回答