我只是想在數據庫中寫一條消息，然后在運行應用程序時出現此錯誤據我所知，我已經在我的 gradle 中添加了必要的依賴項gradle 在模塊級別，我已經添加了 Firebase Core、Firebase 數據庫等：dependencies {    implementation fileTree(include: ['*.jar'], dir: 'libs')    implementation 'com.android.support:appcompat-v7:28.0.0-rc02'    implementation 'com.android.support:design:28.0.0-rc02'    implementation 'com.android.support.constraint:constraint-layout:1.1.3'    implementation 'com.android.support:support-vector-drawable:28.0.0-rc02'    implementation 'com.android.support:support-v4:28.0.0-rc02'    implementation 'com.firebaseui:firebase-ui-auth:5.0.0'    implementation 'com.google.firebase:firebase-database:16.0.1'    implementation 'com.google.firebase:firebase-auth:16.2.1'    implementation 'com.google.android.gms:play-services-maps:16.1.0'    implementation 'com.google.firebase:firebase-core:16.0.8'    testImplementation 'junit:junit:4.12'    androidTestImplementation 'com.android.support.test:runner:1.0.2'    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'    implementation 'com.squareup.picasso:picasso:2.71828'    implementation 'de.hdodenhof:circleimageview:3.0.0'    implementation 'com.github.bumptech.glide:glide:4.9.0'    annotationProcessor 'com.github.bumptech.glide:compiler:4.9.0'    implementation 'com.facebook.android:facebook-android-sdk:[4,5)'    implementation 'com.facebook.android:facebook-android-sdk:4.42.0'    implementation 'com.android.support:multidex:1.0.3'}apply plugin: 'com.google.gms.google-services'項目級別的gradlebuildscript {    repositories {        google()        jcenter()        mavenCentral()    }    dependencies {        classpath 'com.android.tools.build:gradle:3.3.0'        classpath 'com.google.gms:google-services:4.2.0'        // NOTE: Do not place your application dependencies here; they belong        // in the individual module build.gradle files    }}allprojects {    repositories {        google()        jcenter()    }}